what is this 回答 与what is that 回答

我告诉你吧。绝对不能用this 和that来回答。为了避免重复，应该把this和that改为it。即：It is a/an +名词（单数）。It is 可以缩略成It’s。
如：What is this？It’s a book.
又如：What is that？It’s a pen.
跟它类似的还有What are these？ What are those？答语都用They're 不能用These are 和 Those are。

what is this 这是什么
this is ... 这是..
what is that 那是什么
that is... 那是...

what is this 就回答 this is ___. 举例，what is this? this is a pen.
what is that 就回答 that is ___. 举例, what is that? that is a car.

this is ...
that is ...

This is.../It is...
That is.../It is...