老师们，谁能解释一下特殊疑问句的强调句式作宾从的结构，如：teachers don't know

Question

what it is that prevents……

Answer 1

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？
例子 When and where was it that you were born?

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。
例子 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。
例子 Was it yesterday that he met Li Ping?

4.not … until … 句型的强调句
A. 句型为：It is/ was not until + 被强调部分 + that + 其他部分
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.
B. 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。
5.谓语动词的强调
A. 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。
Do be careful when you cross the street. 过马路时，务必（千万）要小心啊！
B. 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。

你的例子错了

参考资料：http://zhidao.baidu.com/question/440008374.html