1. 句型转换。 

1. （1） You should go swimming. (对划线部分提问)

3. （2） They should eat fast food.(变为否定句)

5. （3） I want to stay healthy.(变为一般疑问句)

7. （4） Is it good to surf the Net？(作肯定回答)

9. （5） I think that "playing sports" makes people healthy. (变为否定句)