变复数1.This is a knife2.That is an apple tree3.He is a policeman4.The ruler is mine5.What is his name?6.There is a sheep on the hice?7.Who is that man?

This is a knife.怎样变复数. Is this her knife变复数 This is a knife 改为复数 this is knife in the box（变复数句 This is a box and that is a knife.改为复数形式〔怎么变的〕 Whose knife is this?(改成复数) Is this your knife 改为复数句子 this is my knife改复数句 She has a knife.变复数句 this is a new car.变复数 This is a marker.（变复数） this is a piano怎么变复数 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 （改为复数句） This is a pen and that is a knife改为复数形式 whose knife is this?将句子变成复数 This knife is his.怎么改复数形式的句子? This is pen变复数