强调句是一种修辞，是人们为了表达自己的意愿或情感而使用的一种形式。通过各种方式对句子中的某个部分进行强调，从而起到修辞的作用。 英语常用的强调结构是"It is (was)+被强调部分(主语、宾语或状语)+who (that)..."。
1. It is (was) +被强调部分+that(who)…
为了强调句子的某一成分(通常是主语、宾语或状语)，常用强调结构：It is (was) +被强调部分+that(who)… ，但如果被强调的部分既包括人又包括物，只能用that。表示强调的it在这种结构的句子中作主句的主语。
原始句：Last night I saw a film in the Youth Palace.
强调主语：It was I that (who) saw a film in the Youth Palace last night.
强调宾语：It was a fiml that I saw in the Youth Palace last night.
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强调地点状语：It was in the Youth Palace that I saw a film last night.强调时间状语：It was last night that I saw a film in the Youth Palace.
一般讲，原句的谓语动词如果是现在或将来各种时态，用It is…that (who)…;如果原句谓语动词是过去各种时态，则用It was… that(who)…。
注意点：
①在强调主语时，that后的谓语动词要与被强调者保持人称和数的It is I who am a teacher.
②即使被强调的主语是复数，主句中的谓语动词也用单数It is they who often help me with my lessons.
③在强调时间、地点、原因、或方式状语时，不要用when,where,why或 how ，而用that
It was because her mother was ill that she didn't go with us.
④在强调not … until 结构中由 until 短语(或从句)表示的时间状语时，要用固定的强调句型
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It is(was) not until ...that...。that 从句中的谓语动词用肯定式。
My father didn't come home until 12 o'clock last night.
It was not until 12 o'clock last night that my father came home.
⑤在强调一般疑问句中的某一成分时，主句要用一般疑问句的语序：把is/ was提到it前面。
Did this happen in Beijing?
Was it in Beijing that this happened?
Where were you born?
Where was it that you were born?
⑦not …until…句型的强调句
句型为：It is/ was not until + 被强调部分 + that + 其它部分
原始句：He didn’t go to bed until/ till his wife came back.
强调句：It was not until his wife came back that he went to bed.
此句型只用until，不用till。但如果不是强调句型，till, until可通用;因为句型中It is/ was not … 已经是否定句了，that后面的从句要用肯定句，切勿再用否定句了。
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2. 谓语动词的强调It is/ was … that …结构不能强调谓语，如果需要强调谓语时，用助动词do/ does或did。
Do sit down. 务必请坐。
He did write to you last week.上周他确实给你写了信。
Do be careful when you cross the street.
过马路时，务必(千万)要小心啊!
此种强调只用do/does和did ，没有别的形式;过去时用did，后面的谓语动词用原形。