1、连接词that一般不能省略，但当主句中含动词do的某种形式时，that可以省略。如：
What I want to do is (that) I can go up to him and thank him. 我想做的事是走到身边去感谢他。
2、当句子的主语是：
advice, demand, decision, desire, idea, insistence, instruction, order, plan, proposal, recommendation, request, requirement, suggestion, wish等名词时，表语从句须用虚拟语气，即：should +do。如：
My advice is that you should go to apologize to him. 我的建议是你应该去向他道歉。
连接表语从句的连接词有：that, what, who, when, where, which, why, whether, how, whoever，whichever ，whatever等。还有如because, as if, as though等。
1、His suggestion is that we should stay calm.
他的建议是，我们应该保持冷静。
2、The question is when he can arrive at the hotel.
问题是，他什么时候可以到达酒店。
扩展资料：
一、表语成分：
表语是用来说明主语的身份、性质、品性、特征和状态的，表语常由名词、形容词、副词、介词短语、不定式、动词的-ing、从句来充当。
它常位于系动词（be, become, appear, seem,look,sound,feel,get,smell等词）之后。如果句子的表语也是由一个句子充当的，那么这个充当表语的句子就叫做表语从句。
二、表语从句例句：
1、This is what I want.
这就是我想要的。
2、The reason why he was late is that his bike broke down.
他迟到是因为自行车坏了。
3、Next sunday is when we shall meet.
下周日是我们见面的时间。
4、This is why I am late.
这就是我迟到的原因。
5、My problem is which computer to choose.
我的问题是不知道选哪个电脑好。
参考资料：