英语语法：强调句
一、强调句英语中有时为了需要，经常要强调句子中的某一成分，要用到一些强调句型。
强调句型的基本结构是：
It is/was + 被强调部分(主语、宾语、宾语补足语或状语等) + that/who（当强调主语且主语指人）+句子的其余部分
①连接词
一般说来，如果被强调部分是人时，用连词that或who；被强调的部分是宾语，指人时也可以用whom；如果被强调部分是物，只能用连词that。
It was John and Mike who/that saw Mary in the street last night.
约翰和迈克昨晚在路上看到了玛丽。
It is Mary whom/ who he often helps .
他经常帮助玛丽。
It was in the street that I met him yesterday.
我昨天在路上碰到了他。
②不同的强调成分
正是玛丽昨天在路上遇到一个乞丐。
It was Mary who/that met an old beggar in the street yesterday.
(强调主语)
玛丽昨天在路上遇到一个乞丐。
It was an old beggar whom/that Mary met in the street yesterday.
(强调宾语)
正是昨天玛丽在路上遇到一个乞丐。
It was yesterday that Mary met an old beggar in the street.
(强调时间状语)
昨天正是在路上玛丽遇到一个乞丐。
It was in the street that Mary met an old beggar yesterday.
(强调地点状语)
注意：有时，be前可使用表示推测的情态动词。如：It must be Peter who has let this secret out.一定是彼得将这个秘密泄露出去的。It might be last night that they did their homework.他们也许是昨晚做完作业的。
③时态
如果原句中谓语动词使用的是现在范畴的时态(一般现在时、现在进行时、现在完成/现在完成进行时、一般将来时、将来进行时、将来完成时等)，用It is...that...如果原句中谓语动词为过去范畴的时态(一般过去时、过去进行时、过去完成时、过去将来时等)，则用It was...that...
It's Mary who/that meets an old beggar in the street.
正是玛丽经常在路上见到乞丐。
It's Mary who/that is doing the housework.
正是玛丽正在做家务。
It's Mary who/that has done such terrible things.
正是玛丽做了这件可怕的事情。
It's Mary who/that will have finished this task by the next week.
正是玛丽下个礼拜将会完成这个任务。
It's Mary who/that will be going to America.
正是玛丽将要去美国。
It's Mary who/that will go to see the doctor tomorrow.
正是玛丽明天要去看病。
④总结
构成强调句的it本身没有词义；
强调句中的连接词一般只用that，who，即使在强调时间状语和地点状语时也如此，that，who不可省略；
强调句中的时态只用两种，一般现在时和一般过去时。
原句谓语动词是一般过去时、过去完成时和过去进行时，用It was …… ，其余的时态用It is …… .
二、区分强调句与其他类型从句（主、定、状）
①强调句与主语从句的区别
“It is / was + 形容词/ 分词/+ that从句”
是主语从句，
它译成中文时不可加上
“正是……”“就是……”之类字眼，若删去“It is / was...that...”，则原句不成立。
而强调句型若删去“It is / was...that / who...”，
原句结构与语意均完整，
译成中文时，常可加上“正是……”“就是……”之类字眼。It 为形式主语，等于that后跟部分。
It is true that he is honest. (主语从句)
他真的很诚实。
It is known to all that China is a country with a long history. (主语从句) 众所周知，中国是一个历史悠久的国家。It was here that he fell off his bicycle.(强调句)
这正是他从自行车上摔下来的地方。
几种易混句式与强调句②含有定语从句的强调句型(在被强调的名词后再设计一个以该名词为先行词的定语从句，这时不要把定语从句当作强调句)。
It was this school where (in which) he once studied that gave him a chance of teaching.正是这所他曾经学习过的学校给了他教学的机会。
③强调句型与状语从句的区别
It was at 7:00 that I arrived.(强调句型，强调时间状语at 7:00)
正是在7:00时，我到了。
It was 7:00 when I arrived.(时间状语从句，在7:00前无介词at)
当我到达时，时间是7:00。
It was two years ago that I began to learn drawing.(强调句型，前后时态一致)
正是在两年前我开始学习绘画。
It is(has been) two years since I began to learn drawing.(since引导的时间状语从句，前后时态不一致)
自从我学习绘画以来已经有两年了。
It was two years before they came to see us.(时间状语从句)
过了两年后他们才来看我们。
It was two years later that they came to see us.(强调句型)
