This is a pen.(改为复数形式)

this is a pen.改为复数句 This is a pen.(改为复数形式) This is a pen and that is a knife改为复数形式 This is a pen改为否定句,改为单复数转换改为一般疑问句或提问,肯定句做回答. This is a pen.改为一般疑问句 What's this?It's a pen.(改为复数句) This is pen变复数 is this a red pen 改为复数句,并作肯定回答is that an english book?改为复数句,并作否定回答 What is that?itis a pen改为复数形式 This is a pen 变为复数如题 Is this a pen?（变复数句） This is a pen变为复数句,怎么变 This is a book 改为复数句 This is a pear.改为复数句 this is a book改为复数形式 This is a dress.改为复数形式 this is a tree 改为复数句 Is this a bus （改为复数句