That is a box 改为单数或则复数

That is a box 改为单数或则复数 This is a bus 改为单数或则复数 That is a box 改为复数句子 This is a box.改为复数形式 this is a box改为复数 This is a box and that is a knife （改为复数句） These are english books 改为单数或则复数 is that a box改成复数 把下列句子由单数变为复数或由复数变为单数.1、This is a book.2、That is a box. This book is in that box.（改为复数形式） This is a box and that is a knife.改为复数形式〔怎么变的〕 it is a box.(改为复数形式）帮忙啊!