句型转换。 1. There is a bag on the chair. (改为否定句) There ______ a bag on the chair. 2. There are some bananas on the basket. (改为否定句) There ______ ______ bananas on the basket. 3. There are some cars in front of the tall building. (改为一般疑问句并作否定回答) ______ ______ ______ cars in front of the tall building? ______,  there aren't. 4. There are four students in the classroom. (对划线部分提问) ______ ______ students are there in the classroom?