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 变为复数 Is this a pen?（变复数句） this.is pen变复数句 This is pen变复数 this is a pen.改为复数句 this is a bus.【变为复数句】 she is a teacher.变复数 it is a pen.变复数 this is my It is a pen.变为一般疑问句怎么变? That is a pen.(变为复数) that is a pen (变为复数） this is a piano怎么变复数