句型转换。
①This is my ruler.(改为复数形式)
_____ _____my _____ .
②Are those your sisters?(改为单数形式)
_____ _____your ______ ?
③He is my grandfather.(改为一般疑问句并作肯定回答)
_____ _____ ______grandfather?
_____,_____ _____.
④That is his friend.(改为否定句)
_____ _____ _____friend.