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

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就不可以再出现了哦,
名词变复数一般在名词后面加“s”,但遇到以x,sh,ch等结尾的要加“es”,遇到以f,fe结尾的要改f或fe为v再加es哦,
所以box的复数是boxes,knife的复数形式是knives,
如果还有疑问欢迎再提出来哦~~

These are boxes and those are knives。
This—These
is——are
a box—boxes
that——those
a knife——knives
唔，这些都是固定的改法，记住就行了~