that's an eraser ______ _____an eraser?(一般疑问句) this is a cup (攺为复数形式)

问题描述:

that's an eraser ______ _____an eraser?(一般疑问句) this is a cup (攺为复数形式)
those are (red books)提问_______ ________ those
they are (my sisters and brothers)提问______ ______ ______?

如下
It that an eraser?
These are cups.
What are those?
Who are they?