21. 陈述部分的主语this ,that,简略问句用it:陈述部分的主语these, those,简略问句的主语用they.

This is my pen, isn't it?

22. 在"none of…"结构中，如of 后的名词或代词是单数，后面的主语也为单数，这种情况，主要由于of 后的名词或代词为不可数名词

None of it is here, is it?

23. 陈述部分如是"each of "结构作主语，若强调个别，简略问句的主语用单数代词；若强调全体，简略问句用复数代词。

In our class each of the students passed the exam, didn't he/they?

24. 陈述部分含ought to 时，简略问句要用should,也可重复ought.

We ought to make a greater contribution to the world revolution, shouldn't/oughtn't we?

25. 陈述部分的谓语含有dare, need时，看它们是情态动词还是行为动词，分别重复dare, need或 用do 的适当形式。

The girl daren't go home alone, dare she?