If的用法
if的条件从句分为真实条件从句和虚拟条件从句.
真实条件从句：真实条件从句适用于主将从现,是假设有可能发生的.
一.位置
在if引导的条件状语从句中,既可以放在主句之前,也可以放在主句之后.假设if条件句
放句首,从句后面要加逗号,和主句隔开.
You will catch the bus if you get up early. = If you get up early, you will catch the bus.
二.时态
1.〔主祈从现〕
主句：一般现在时态〔包含祈使句和含有情态动词can, may, must等的句子〕
从句：一般现在时态
2.〔主将从现〕
主句：一般将来时态
从句：一般现在时态
3.从句：现在进行时,主句：一般将来时
If you are looking for Peter you ' find him upstairs.如果你是在找彼得,上楼就会找到他.
4. if从句用现在完成时,主句用一般将来时
If you have finished dinner I' alsk the waiter for the bill.如果你吃完了,我就叫效劳生来算账
5.if条件句谈论的是重复发生和预示要发生的情景和事件,那么主从句大多用一般现在时态.
如：If bears are in danger ,they attack people.
三.考前须知
1.在if引导的条件状语从句中,当主句是一般将来时态时,不能使用be going to结构,
而要用will.
2.在if引导的条件状语从句中,不能使用some,而要用any.
四.同义句转化
1.借助于祈使句+and/or+简单句转化,and表示顺承,or表示转折.
例如：〔1〕If you work hard,you 'll pass the exam.
Work hard, and you 'll pass the exam.
(2)If you do n't hurry up, you 'll be late.
Hurry up, or you 'll be late.
2.借助于介词with或者without来转换
例如：If you help me, I 'll finish my job soon.
With your help , I 'll finish my job soon.
if条件句不一般,几个要点记心间条件句,放在前,逗号要放句中间.条件句表可能,主句多用将来时；条件句表事实,主句常用现在时.
虚拟条件从句：虚拟条件从句是假设不太可能发生的.
IF的虚拟语气有三种：
内容从句主句
与现在事实相反动词过去式〔be用were〕would/could/should/might+动原
与将来事实相反should/were to+ 动原would/could/should/might+ 动原
与过去事实相反had+过分would/could/should/might+ have+ 过分下面三句依次是上面三种情况的例句：If I were you ,I would/could/should/might do that.
If I had know that yesterday I would/could/should/might have told you .
If it should rain , the crops would/could/might be saved.
If引导的宾语从句
一.if引导宾语从句时,意思为：是否,从句的时态通常要和主句保持一致.
【例句】I want to know if he lives there. 我想知道他是否住在那儿.He asked me if I could
help him.他问我是否能帮他.
【考查点】if、whether引导的宾语从句的区别1. if或whether引导宾语从句时,作“是否"
讲,常放在动词ask、see> say、know和find out等后面.一般情况下,两者常可换用,在口语中多用if. 【例句】Nobody knows whether / if it will rain tomorrow.没有人知道明天是否下雨.
Lucy asked whether / if they had a cotton sweater.露西问他们是否有棉制的毛衣.
二.考前须知：if或whether引导宾语从句时,要注意三个方面,即连词、语序和时态.
1. if或whether既不能和that或其他连词(副词)同时使用,也不能省略.
【例句】我不知道他今天是否会来.
［误］I don ' t know that if(whether) he will come here today.
［正］I don ' t know if(whether) he will come here today.他走过来看看猫是否出了毛病.
［误］He came to see what if (whether) there was anything wrong with his cat .
［正］He came to see if (whether) there was anything wrong with his cat .
2.1f或whether引导宾语从句时,虽具有疑问的意义,但其从句应用陈述句的语序.
【例句】Did you know the way to the hospital? The old woman asked me.
The old woman asked me if / whether I knew the way to the hospital.老妇人问我是否知道去医
院的路.
3. if或whether引导的宾语从句应和主句的时态保持一致.
即主句为一般现在时,从句用任一种时态；
主句为一般过去时,从句那么用过去时中的任一种时态.
【例句】I don ' t know if (whether) he has come here.我不知道他是否来过这儿.
Tom asked if (whether) I had read the book.汤姆问我是否看过这本书.
三.If和whether两者不能互换的情况
1.只能用whether的情况在动词不定式之前只能用whether：
【例句】I can' t decide whether to stay.我不能决定是否留下.
2.在whether - or not的固定搭配中：
【例句】I want to know whether it ; s good news or not. 我想知道它是不是好消息.
3.在介词后,只能用whether ：
［例句］His father is worried about whether he loses his work.
他的父亲担忧他是否会失去工作.
4.用if会引起歧义时：
【例句】Could you tell me if you know the answer?这句话有两种意思：“你能告诉我
你是否知道答案吗？〞或“如果你知道答案,请告诉我,好吗？".如用whether那么可防止
歧义.
【考题链接】I don ' t know they could pass the exam or not.
A. why
B. if
C. that
D. whether
答案：D 解题思路：此题考查if与whether的区另1J,在whether--• or not的固定搭配中通常只用whethero
练习题：
句型转换 1. Do they want fried chicken? He asked the boys.(改为宾语从句)
He asked the boys they fried chicken.
2.Was the watch made in Shanghai? I don' t know.(改为宾语从句)
I don' t know the watch made in Shanghai.
3.“Do you want to try something new? " Tom' s mother asked him.(同义句转换)
Tom' s mother asked him to try something new.
答案：1. if / whether, wanted 2. if / whether, was 3. if / whether he wanted 一、用所给词的适当形式填空
1.If you(feel) tired, you(have) to have a rest.
3. If there(be) fewer trees, there( be) more pollution.
5.If Marcia(live) alone, she( keep) a pet parrot.
https://www.doczj.com/doc/f219236749.html,na( buy) a new dress if the old one(be) out of style.
9. Peter( send) me a beautiful souvenir if he(tour) Spain.
10. If Mr Green(say) I am hard- working, my parents( feel) glad.
11.I(go) to the beach if it( not rain) this week.
13.He(write) a letter to his grandparents if he(get) his report card this week.
14. If she(get) up late, she( not catch) the early bus.
15. Peter(major) in English if he(pass) the exams in Peking University.
16.如果努力学习,你就会取得好成绩.
If you, you good.
17.他如果看电视太久了,他的父母会不快乐.
If he TV too much, his parents unhappy.
18.如果我们为他组织生日聚会,大家都会来的.
Everyone if we a birthday party him.
19.如果明天不下雨,我会和你一起去公园的.
If it tomorrow, I go to the park you.
21.如果他有空,他会帮助你的.
If he, he you.
23.你如果抄同学的作业就不能学好各门功课.
You good at all the subjects if you the other students homework.
I单项选择〔
1.If you to the party, you ' have a great time.
A. will go
B. went
C. go
D. going
2.It will be a long time Peter his work.
A. since, has finished
B. after, finishes
C. when, will finish
D. before, finishes.
3.What will father us from Japan?
A. take
B. bring
C. carry
D. make
4.Weifang is famous kites.
A. for
B. to
C. on
D. with
5.I her the answer if she me.
A. can tell, will ask
B. will tell, will ask
C. would tell, ask
D. will tell, asks
6.- What are you going to do tomorrow?
--Wd lgo to the library tomorrow if it.
A. isn 'rain
B. rain
C. won' rain
D. doesn , rain
7.— Do you know when he will come back tomorrow?
--Sorry, I don ' know. When he back, I ' tell you.
A. comes
B. will come
C. come
D. may come
8.What will you do if you to the old folk ' home visit?
A. go
B. went
C. going
D. will go
9.If I eat food, I ' ble very fat.
A. too many
B. many too
C. too much
D. much too
10.I ' glive the book to him if he here next Sunday.
A. will come
B. comes
C. is coming
D. came
11.There an English film in our school tomorrow.
A. is going to have
B. will have
C. is going to be
D. has
12.Could you tell us where ?
A.will the next Olympic Games held
B.the next Olympic Games will be held
C.would the next Olympic Games be held
D.the next Olympic Games would be held
13.When my mother returned last night, I a book.
A. read
B. am reading
C. was reading
D. am going to read
14.What you when it began to rain?
A. do, do
B. were, doing
C. are, doing
D. did, do
15.I ' wake you up when he back.
A. will
B. is going to come
C. comes
D. come
1---5 CDBAD
6---10 DAACB
11---15 CBCBC
重点、难点 1. 含有if引导的条件状语从句的复合句中主从句的时态。 2. If引导的宾语从句与条件状语从句的区别。 考情分析 通常在单项选择、完形填空或补全、完成句子等题型中考查，分值约3—4分。 知能提升 （一）知识讲解 【认知讲解】 I. if引导的宾语从句 if 引导宾语从句时，意思为：是否，从句的时态通常要和主句保持一致。 【例句】 I want to know if he lives there. 我想知道他是否住在那儿。 He asked me if I could help him. 他问我是否能帮他。 【考查点】if、whether引导的宾语从句的区别 1. if或whether引导宾语从句时，作“是否”讲，常放在动词ask、see、say、know和find out等后面。一般情况下，两者常可换用，在口语中多用if。 【例句】 Nobody knows whether / if it will rain tomorrow. 没有人知道明天是否下雨。 Lucy asked whether / if they had a cotton sweater. 露西问他们是否有棉制的毛衣。 2. if或whether引导宾语从句时，要注意三个方面，即连词、语序和时态。 if或whether既不能和that 或其他连词（副词）同时使用，也不能省略。 【例句】 我不知道他今天是否会来。 [误] I don’t know that if(whether) he will come here today. [正] I don’t know if(whether) he will come here today. 他走过来看看猫是否出了毛病。 [误] He came to see what if (whether) there was anything wrong with his cat . [正] He came to see if (whether) there was anything wrong with his cat . if或whether引导宾语从句时，虽具有疑问的意义，但其从句应用陈述句的语序。 【例句】 Did you know the way to the hospital?The old woman asked me. The old woman asked me if / whether I knew the way to the hospital. 老妇人问我是否知道去医院的路。 if或whether引导的宾语从句应和主句的时态保持一致。即主句为一般现在时，从句用任一种时态；主句为一般过去时，从句则用过去时中的任一种时态。 【例句】 I don’t know if (whether) he has come here. 我不知道他是否来过这儿。
中考If引导的两种从句（宾语从句和条件状语从句） If引导的两种从句(宾语从句和条件状语从句) 重点、难点 1. 含有if引导的条件状语从句的复合句中主从句的时态。 2. If引导的宾语从句与条件状语从句的区别。 考情分析 通常在单项选择、完形填空或补全、完成句子等题型中考查。 知能提升 （一）知识讲解 【认知讲解】 I. if引导的宾语从句 if 引导宾语从句时，意思为：是否，从句的时态通常要和主句保持一致。 【例句】 I want to know if he lives there. 我想知道他是否住在那儿。 He asked me if I could help him. 他问我是否能帮他。 【考查点】if、whether引导的宾语从句的区别 1. if或whether引导宾语从句时，作“是否”讲，常放在动词ask、see、say、know和find out等后面。一般情况下，两者常可换用，在口语中多用if。 【例句】 Nobody knows whether / if it will rain tomorrow. 没有人知道明天是否下雨。 Lucy asked whether / if they had a cotton sweater. 露西问他们是否有棉制的毛衣。 2. if或whether引导宾语从句时，要注意三个方面，即连词、语序和时态。 if或whether既不能和that 或其他连词（副词）同时使用，也不能省略。 【例句】 我不知道他今天是否会来。 [误] I don’t know that if(whether) he will come here today. [正] I don’t know if(whether) he will come her e today. 他走过来看看猫是否出了毛病。 [误] He came to see what if (whether) there was anything wrong with his cat . [正] He came to see if (whether) there was anything wrong with his cat . if或whether引导宾语从句时，虽具有疑问的意义，但其从句应用陈述句的语序。 【例句】 Did you know the way to the hospital? The old woman asked me.
If引导的宾语从句和条件状语从句之五兆芳芳创作【重点、难点】 1. 含有if引导的条件状语从句的复合句中主从句的时态. 2. If引导的宾语从句与条件状语从句的区别. 【考情阐发】 通常在单项选择、完形填空或补全、完成句子等题型中考查，分值约3—4分. 【知识讲授】 宾语从句 【例句】I want to know if he lives there. He asked me if I could help him. 【考查点】if、whether引导的宾语从句的区别：从寄义、连词、语序和时态等方面区分. 1.寄义 if或whether引导宾语从句时，作“是否”讲，两者常可换用，在口语中多用if. 【例句】Nobody knows whether / if it will rain tomorrow. Lucy asked whether / if they had a cotton sweater. 2.与连词（副词）关系 if或whether既不克不及和that 或其他连词（副词）同
时使用，也不克不及省略. 【例句】[误] I don’t know that if(whether) he will come here today. [正] I don’t know if(whether) he will come here today. [误] He came to see what if (whether) there was anything wrong with his cat . [正] He came to see if (whether) there was anything wrong with his cat . 3.语序 if或whether引导宾语从句时，虽具有疑问的意义，但其从句应用陈述句的语序. 【例句】The old woman asked me if / whether I knew the way to the hospital. 4.时态 if或whether引导的宾语从句应和主句的时态保持一致.即主句为一般现在时，从句用任一种时态；主句为一般过来时，从句则用过来时中的任一种时态. 【例句】I don’t know if (whether) he ha s come here. Tom asked if (whether) I had read the book. 5.只能用whether的情况 （1）在动词不定式之前只能用whether
If引诱的宾语从句和前提状语从句 【重点.难点】 1. 含有if引诱的前提状语从句的复合句中主从句的时态. 2. If引诱的宾语从句与前提状语从句的差别. 【考情剖析】 平日在单项选择.完形填空或补全.完成句子等题型中考核,分值约 3—4分. 【常识讲授】 宾语从句 句保持一致. 【例句】I want to know if he lives there. He asked me if I could help him. 【考核点】if.whether引诱的宾语从句的差别：从寄义.连词.语 序和时态等方面区分. 1.寄义 if或whether引诱宾语从句时,作“是否”讲,两者常可换用, 在白话中多用if. 【例句】Nobody knows whether / if it will rain tomorrow. Lucy asked whether / if they had a cotton sweater. 2.与连词（副词）关系
if或whether既不克不及和that 或其他连词（副词）同时运用,也不克不及省略. 【例句】[误] I don’t know that if(whether) he will come here today. [正] I don’t know if(whether) he will come here today. [误] He came to see what if (whether) there was anything wrong with his cat . [正] He came to see if (whether) there was anything wrong with his cat . 3.语序 if或whether引诱宾语从句时,虽具有疑问的意义,但其从句运用陈述句的语序. 【例句】The old woman asked me if / whether I knew the way to the hospital. 4.时态 if或whether引诱的宾语从句应和主句的时态保持一致.即主句为一般如今时,从句用任一种时态;主句为一般曩昔时,从句则用曩昔时中的任一种时态. 【例句】I don’t know if (whether) he has come here. Tom asked if (whether) I had read the book. 5.只能用whether的情形
If的用法 if的条件从句分为真实条件从句和虚拟条件从句。 真实条件从句： 真实条件从句适用于主将从现，是假设有可能发生的。 一. 位置 在if引导的条件状语从句中，既可以放在主句之前，也可以放在主句之后。若if条件句放句首，从句后面要加逗号，和主句隔开。 You will catch the bus if you get up early. = If you get up early, you will catch the bus. 二. 时态 1. （主祈从现） 主句： 一般现在时态（包含祈使句和含有情态动词can, may, must等的句子） 从句： 一般现在时态 2. （主将从现） 主句： 一般将来时态 从句： 一般现在时态 3. 从句：
现在进行时，主句： 一般将来时 If you are looking for Peteryou ' llfind 自眇晦编£我彼得，上楼就 会找到他。 4. if从句用现在完成时，主句用一般将来时 If you have finished dinnerl ' llask the waiter fo^lthebi吃完了，我就叫服务生来算账 5.if条件句谈论的是重复发生和预示要发生的情景和事件，则主从句大多用一般现在时态。 如： If bears are in danger ,they attack people. 三. 注意事项 1. 在if引导的条件状语从句中，当主句是一般将来时态时，不能使用be going to结构，而要用will. 2. 在if引导的条件状语从句中，不能使用some,而要用any. 四. 同义句转化 1. 借助于祈使句+and / o筒单句转化，and表示顺承，or表示转折。 例如： (1) lf you work hard,you ' ll pass the exam. Work hard, and you ' ll pass the exam. (2) lf you don ' t hurry up, you ' ll be late. Hurry up, or you ' ll be late.
I f引导的宾语从句和条件状语从句Yesterday disappeared, January 6, 2020
If引导的宾语从句和条件状语从句 重点、难点 1. 含有if引导的条件状语从句的复合句中主从句的时态; 2. If引导的宾语从句与条件状语从句的区别; 考情分析 通常在单项选择、完形填空或补全、完成句子等题型中考查,分值约3—4分; 知识讲解 if引导的宾语从句 if意思为：是否,从句的时态通常要和主句保持一致; 例句I want to know if he lives there. He asked me if I could help him. 考查点if、whether引导的宾语从句的区别：从含义、连词、语序和时态等方面区分; 1.含义 if或whether引导宾语从句时,作“是否”讲,两者常可换用,在口语中多用if; 例句Nobody knows whether / if it will rain tomorrow. Lucy asked whether / if they had a cotton sweater. 2.与连词副词关系 if或whether既不能和that 或其他连词副词同时使用,也不能省略; 例句误I don’t know that ifwhether he will come here today. 正I don’t know ifwhether he will come here today. 误 He came to see what if whether there was anything wrong with his cat . 正 He came to see if whether there was anything wrong with his cat . 3.语序 if或whether引导宾语从句时,虽具有疑问的意义,但其从句应用陈述句的语序; 例句The old woman asked me if / whether I knew the way to the hospital.
重点、难点 1.含有 if 指引的条件状语从句的复合句中主从句的时态。 2.If 指引的宾语从句与条件状语从句的差别。 考情剖析 往常在单项选择、完形填空或补全、达成句子等题型中考察，分值约3— 4 分。 知能提高 （一）知识解说 【认知解说】 I. if 指引的宾语从句 if 指引宾语从句时，意思为：能否，从句的时态往常要和主句保持一致。 【例句】 I want to know if he lives there.我想知道他能否住在那边。 He asked me if I could help him.他问我能否能帮他。 【考察点】 if、 whether 指引的宾语从句的差别 1. if 或 whether 指引宾语从句时，作“能否”讲，常放在动词ask、see、say、know 和 find out 等后边。一般状况下，二者常可换用，在口语中多用if。 【例句】 Nobody knows whether / if it will rain tomorrow. 没有人知道明日能否下雨。 Lucy asked whether / if they had a cotton sweater. 露西问他们能否有棉制的毛衣。 2.if 或 whether 指引宾语从句时，要注意三个方面，即连词、语序和时态。 if 或 whether 既不可以和t hat或其余连词（副词）同时使用，也不可以省略。 【例句】 我不知道他今日能否会来。 [误 ] I don’ t know that if(whether) he will come here today. [正 ] I don’ t know if(whether) he will come here today. 他走过来看看猫能否出了缺点。 [误 ] He came to see what if (whether) there was anything wrong with his cat . [正 ] He came to see if (whether) there was anything wrong with his cat . if 或 whether 指引宾语从句时，虽拥有疑问的意义，但其从句应用陈说句的语序。 【例句】 Did you know the way to the hospital The old woman asked me if / whether The old woman asked me. I knew the way to the hospital. 老太婆问我能否知道去医院的路。 if 或 whether 指引的宾语从句应和主句的时态保持一致。即主句为一般此刻时，从句用任一种时态；主句为一般过去时，从句则用过去时中的任一种时态。 【例句】 I don’ t know if (whether) he has come here. 我不知道他能否来过这儿。
重点、难点 1、含有if引导的条件状语从句的复合句中主从句的时态。 2、If引导的宾语从句与条件状语从句的区别。 考情分析 通常在单项选择、完形填空或补全、完成句子等题型中考查,分值约3—4分。 知能提升 (一)知识讲解 【认知讲解】 I. if引导的宾语从句 if 引导宾语从句时,意思为:就是否,从句的时态通常要与主句保持一致。 【例句】 I want to know if he lives there、我想知道她就是否住在那儿。 He asked me if I could help him、她问我就是否能帮她。 【考查点】if、whether引导的宾语从句的区别 1、if或whether引导宾语从句时,作“就是否”讲,常放在动词ask、see、say、know与find out等后面。一般情况下,两者常可换用,在口语中多用if。 【例句】 Nobody knows whether / if it will rain tomorrow、 没有人知道明天就是否下雨。 Lucy asked whether / if they had a cotton sweater、 露西问她们就是否有棉制的毛衣。 2、if或whether引导宾语从句时,要注意三个方面,即连词、语序与时态。 if或whether既不能与that 或其她连词(副词)同时使用,也不能省略。 【例句】 我不知道她今天就是否会来。 [误] I don’t know that if(whether) he will come here today、 [正] I don’t know if(whether) he will come here today、 她走过来瞧瞧猫就是否出了毛病。 [误] He came to see what if (whether) there was anything wrong with his cat 、 [正] He came to see if (whether) there was anything wrong with his cat 、 if或whether引导宾语从句时,虽具有疑问的意义,但其从句应用陈述句的语序。 【例句】 Did you know the way to the hospital?The old woman asked me、 The old woman asked me if / whether I knew the way to the hospital、 老妇人问我就是否知道去医院的路。 if或whether引导的宾语从句应与主句的时态保持一致。即主句为一般现在时,从句用任一种时态;主句为一般过去时,从句则用过去时中的任一种时态。 【例句】 I don’t know if (whether) he has come here、 我不知道她就是否来过这儿。
重点、难点之杨若古兰创作 1. 含有if引诱的条件状语从句的复合句中主从句的时态. 2. If引诱的宾语从句与条件状语从句的区别. 考情分析 通常在单项选择、完形填空或补全、完成句子等题型中考查，分值约3—4分. 知能提升 （一）常识讲解 【认知讲解】 I. if引诱的宾语从句 if 引诱宾语从句时，意思为：是否，从句的时态通常要和主句坚持分歧. 【例句】 I want to know if he lives there.我想晓得他是否住在那儿. He asked me if I could help him.他问我是否能帮他. 【考查点】if、whether引诱的宾语从句的区别 1. if或whether引诱宾语从句时，作“是否”讲，常放在动词ask、see、say、know和find out等后面.普通情况下，两者常可换用，在口语中多用if. 【例句】 Nobody knows whether / if it will rain tomorrow. 没有人晓得明天是否下雨. Lucy asked whether / if they had a cotton sweater. 露西问他们是否有棉制的毛衣. 2. if或whether引诱宾语从句时，要留意三个方面，即连词、语序和时态. if或whether既不克不及和that 或其他连词（副词）同时使用，也不克不及省略. 【例句】
我不晓得他今天是否会来. [误]I don’t know that if(whether) he will come here today. [正]I don’t know if(whether) he will come here today. 他走过来看看猫是否出了毛病. [误]He came to see what if (whether) there was anything wrong with his cat . [正] He came to see if (whether) there was anything wrong with his cat . if或whether引诱宾语从句时，虽具有疑问的意义，但其从句利用陈述句的语序. 【例句】 Did you know the way to the hospital? The old woman asked me. The old woman asked me if / whether I knew the way to the hospital. 老妇人问我是否晓得去病院的路. if或whether引诱的宾语从句应和主句的时态坚持分歧.即主句为普通此刻时，从句用任一种时态；主句为普通过去时，从句则用过去时中的任一种时态. 【例句】 I don’t know if (whether) he has come here. 我不晓得他是否来过这儿. Tom asked if (whether) I had read the book. 汤姆问我是否看过这本书. 3. 只能用whether的情况 在动词不定式之前只能用whether： 【例句】 I can’t decide whether to stay. 我不克不及决定是否留下.
重点、难点之宇文皓月创作 1. 含有if引导的条件状语从句的复合句中主从句的时态。 2. If引导的宾语从句与条件状语从句的区别。 考情分析 通常在单项选择、完形填空或补全、完成句子等题型中考查，分值约3—4分。 知能提升 （一）知识讲解 【认知讲解】 I. if引导的宾语从句 if 引导宾语从句时，意思为：是否，从句的时态通常要和主句坚持一致。 【例句】 I want to know if he lives there. 我想知道他是否住在那儿。 He asked me if I could help him. 他问我是否能帮他。 【考查点】if、whether引导的宾语从句的区别 1. if或whether引导宾语从句时，作“是否”讲，常放在动词ask、see、say、know和find out等后面。一般情况下，两者常可换用，在口语中多用if。 【例句】 Nobody knows whether / if it will rain tomorrow. 没有人知道明天是否下雨。 Lucy asked whether / if they had a cotton sweater. 露西问他们是否有棉制的毛衣。 2. if或whether引导宾语从句时，要注意三个方面，即连词、语序和时态。 if或whether既不克不及和that 或其他连词（副词）同时使用，也不克不及省略。 【例句】 我不知道他今天是否会来。 [误]I don’t know that if(whether) he will come here today. [正]I don’t know if(whether) he will come here