肯定、疑问、否定
肯定句
还疑问句、否定
最近肯定、否定、疑问句
几次
用法一：表示过去发生或已经完成的某一动作对现在造成的影响或结果。常与just（刚刚），already（已经），never（从来没有），ever（曾经），before（以前），yet（仍然），once（一次），twice（两次），many times （很多次），how many times（多少次），so far（迄今为止），during the past（last）three years（最近三年来）等连用。
※副词的位置：①just常用于肯定句中，放在have / has后，He has just come .
②never表示否定, 放在have / has后, He has never visited the Great Wall.
③ever用于疑问句中,句型为: Have / Has＋主语＋ever ＋过去分词？“…曾经……过吗？”用于询问某人过去的经历。Have you ever been to the farm？
④before用于句末，The woman has never heard of that before.
⑤yet 用于句末或not 之后.Has the train arrived yet? No, not yet.
⑥already用于肯定句, have / has 之后或句末.We have already finished it.
⑦so far用于句首或句末. So far, we have visited the moon.
用法二：表示过去已经开始，一直延续到现在的动作或状态。时间状语有：
①for＋表示一段时间的词语I have taught English for 19 years。
②since＋表示过去时间点的词语He has been at this school since 1986.
③since＋表示过去的时间状语从句I have lived here since I was born.
2 ④since＋一段时间＋ago. I have known him since 20 years ago.
三、现在完成时态中可以和表示一段时间状语（for，since，how long, all one’s life）连用的动词必须是表示延
续的情况或动作的动词，即延续性动词。如：be，have，know，live，work，study，learn，teach，keep，speak，talk，draw，wait，wear，walk，sleep，drive，write，do，clean等。
I have been a teacher for nearly 20 years. How long has he lived here?
英语中还有一些动词的意义决定它们所表示的动作不能延续,只是一瞬间
就结束的动作,这类动词叫做“非延续性动词”，常见的有：come，go，arrive，reach，see，hear，close，open，leave，begin，start，lose，buy，fall，join，die，get up，become，borrow，lend，find，finish，receive等。这
些动词可用于现在完成时，说明某个动作的结果还存在，但不能和表示一段时间的状语（how long，for，since）
连用。He has come back.（√）He has come back for two hours.（×）
※但在否定句中，非延续性动词也可用表示一段时间的状语来修饰，如
I haven’t heard from my father for a long time. We haven’t seen him since 1999.
（5）用相应的延续性动词替代非延续性动词。
He has bought the book for two weeks. 改为:He has had the book for two weeks.
常见的相应转换形式如下:
borrow / lend→keep, buy→have, finish / end→be over,
arrive /come / go / move / reach /get to→be in /at / be here /be there,
begin / start→be on , open→be open , close→be closed,die→be dead ,
leave→be away（from）, go to school→be in school / be a stu dent,
getup→be up, fall asleep→be asleep , fall ill→be ill, get to know→know,
lose→be lost,become→be, return / come back / get back→be back,
join→be in / be a…member, join the army→be in the army /be a soldier,
receive / get a letter→have a letter , catch / get a cold→have a cold,
begin to study→study,
他参军已有三年.He has joined the army for three years.（错）改为:
He has been in the army for three years / since three years ago.
He has been a soldier for three years / since three years ago.
He joined the army three years ago.
It is three years since he joined the army.
Three years has passed since he joined the army.
