把This is a box and that is a knife.改成复数形式

把This is a box and that is a knife.改成复数形式 This is a box and that is a knife.改为复数形式〔怎么变的〕 This is a box and that is a knife （改为复数句） This is a pen and that is a knife改为复数形式 is that a box改成复数 This is a box.改为复数形式 This is a book and that is a knife 改为复数句 Plrase put the clot 把下列句子该形式改为复数形式There is a knife in the box.Our teacher often that is a biack knife的复数形式是什么 What is this? It is a box.复数形式 This is a knife 改为复数 This is a knife.怎样变复数.