强调句和主语从句的关系，答案必须是正确的，请详述

强调句将句子中的it is / was …that同时省去,句子仍然成立；而主语从句将that与后面部分代替it，成立。如：
(1) It is Li Lei’s brother that you met in the street yesterday. 你昨天在街上所见到的就是李蕾的兄弟。
本句若将It is 及 that同时省去为：You met Li Lei’s brother in the street yesterday. 句子同样成立,因此前面的句子是强调句型。
(2) It is exciting that we have succeeded in sending up Shenzhou V. 我们成功地发射了神舟五号这件事情真令人兴奋。
本句若将It is 及 that同时省去为：We have succeeded exciting in sending up Shenzhou V. 显然句子错误,因此,前面句子不是强调句型,而是主语从句。

强调句和主语从句是两种完全不同的句型。强调句只能由It +be...that/who引导，这里，it's和that/who只是一种结构框架，没有实际意义的。而主语从句可以用when/where/why/that/what/how/whether/who引导。比如：when to start is still unsure/where I am is none of your business.注意主语是陈述语气。

而主语从句，从句在整个复合句的结构当中是充当主语的，而强调句则不行，所以为什么去掉it is / was …that句子仍然成立