语法讲解：强调句

   一、强调句句型
    1. 陈述句的强调句型：it is/ was + 被强调部分（通常是主语、宾语或状语）+ that/ who（当强调主语且主语指人）+ 其他部分。
    e.g. it was yesterday that he met li ping.
    2. 一般疑问句的强调句型：同上，只是把is/ was提到it前面。
    e.g. was it yesterday that he met li ping？
    3. 特殊疑问句的强调句型：被强调部分（通常是疑问代词或疑问副词）+ is/ was + it + that/ who + 其他部分？
    e.g. when and where was it that you were born？
    4. 强调句例句：针对i met li ming at the railway station yesterday.句子进行强调。
    强调主语：it was i that （who） met li ming at the railway station yesterday.
    强调宾语：it was li ming that i met at the railway station yesterday.
    强调地点状语：it was at the railway station that i met li ming yesterday.
    强调时间状语：it was yesterday that i met li ming at the railway station.
    5. 注意：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、not … until … 句型的强调句
    1. 句型为：it is/ was not until + 被强调部分 + that + 其他部分
    e.g. 普通句：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.
    2. 注意：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。
    三、谓语动词的强调
    1. 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.
    e.g. 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！
    2. 注意：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。