This is Mary怎么变为复数?

This is Mary怎么变为复数? This is a pen变为复数句,怎么变 This is my sister(变为复数句) this is a bus.【变为复数句】 This is an apple 变为复数句子 Is this your book ? 变为复数句 This is a key.(变为复数) This is not Mary's dress.(变为一般疑问句） Is this a car?复数Is this a car?(变为复数） Yes,it is.（变为复数） This is my watch.怎么变特殊疑问句变为复数句又是怎样的？ is this mary‘s doll?将句子变成复数 this is a boy is schoolbag 变为复数形式 What is this It is a photo.变为复数形式 This is my good friend 变为复数句 This is a pen 变为复数如题 This book is very interesting（变为复数句） Who is this little boy?变为复数句 This man is very busy.变为复数快