题目内容：

This is a box and that is a knife.改为复数形式〔怎么变的〕

优质解答

These are boxes and those are knives.指示代词this that都是单数,应改为复数,this（这）的复数为these（这些）,that (那)的复数为those(那些),谓语动词is是单数,应该改为复数are,名词也应该相应地改为复数,所以a就...