按要求完成下列各题
【小题1】Every year it receives over 750，000 visitors. (改为同义句)
It receives ________________ 750，000 visitors every year.
【小题2】The beautiful sweater on the bed is his sister's. (改为同义句)
The beautiful sweater on the bed ________ ________ his sister.
【小题3】Charlie is so young that he can't take the underground alone. (改为简单句)
Charlie is ________________ to take the underground alone.
【小题4】Mrs. Black often stops her son playing computer games. (改为同义句)
Mrs.  Black often ________ her son ________ ________ computer games.
【小题5】Someone is knocking at my door.  It must be Tom. (合并为一句)
It ________ be Tom ________ at my door.