whose knife is this?将句子变成复数

whose knife is this?将句子变成复数 Whose knife is this?(改成复数) Is this your knife 改为复数句子 将下列句子变成复数形式：This is my sister. is this mary‘s doll?将句子变成复数 This knife is his.怎么改复数形式的句子? Is this her knife变复数 This is a knife 改为复数 this is my knife改复数句 This is a knife.怎样变复数. knife变成复数! 将句子变成复数形式4、 将下列句子变成复数形式1) This is a bus .2) She has a nice d