This is a pen变为复数句,怎么变

This is a pen变为复数句,怎么变 this is a pen.改为复数句 This is a pen 变为复数如题 this is a bus.【变为复数句】 Is this a pen?（变复数句） That is a pen.(变为复数) that is a pen (变为复数） this.is pen变复数句 This is a pen.(改为复数形式) This is my sister(变为复数句) Is this your book ? 变为复数句 What is this?变为复数句___________________________.It is an arm.变为复数句___________________________.This is a foot.变为复数句___________________________.What are these?变为单数句___________________________.These are bags.变为 there is a pen on the desk 变为复数 is this your pen（变为肯定句） This is a key.(变为复数) 英语 改复数句This is a pen.Is this your backpack?It's a black bag This is pen变复数 It is a watch.变为复数句