this is a pen.改为复数句

this is a pen.改为复数句 This is a pen.(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. What's this?It's a pen.(改为复数句) 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 This is a book 改为复数句 This is a pear.改为复数句 this is a tree 改为复数句 Is this a bus （改为复数句 this is a shirt改为复数句 this is a watch(改为复数句) This is a shirt .改为复数句 this is a pencil改为复数句 This is a butterfly改为复数句 this is a letter改为复数句 This is a dog :改为复数句 Is this a pen?（变复数句） This is a pen变为复数句,怎么变