Who is this/that? 回答时是不应该重复this或that的，而应该用人称代词。如果this或that指的是人，而且此人的性别清楚可变，this或that实为this man/woman或that man/woman的省略，则用he或she来回答。如果此人性别难以区分，则用中性代词it。
电话中问 Who is that? 回答为This is XXX speaking.
如:
A（敲门）
B：Who is that？
A:It's Eva.(或I'am Eva)
2、打电话的时候
A（打电话）
B：（接电话）Who is that?
A:This is Eva
3、日常交谈,问“他/她/那是谁?”
A：Who is that?
B :He/She is Eva.(或That is my sister)
也有这么说的：
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。
