低瓦斯矿井中，相对瓦斯涌出量大于（）m³/t或有瓦斯喷出的个别区域（采区或工作面）为高瓦斯区，该区应按高瓦斯矿井管理。

A、10

B、5

C、40

D、20

句型转换。

1. He used to go swimming in this river. (改为一般疑问句)

    _____ he _____ to go swimming in this river?

2. He used to be afraid of the dark. (对画线部分提问) 

    _____ _____ he _____ to be afraid of?

3. I have to study for the test. (对画线部分提问)

    _____ _____ you have to _____ for?

4. My biggest problem is that I'm too busy. (对画线部分提问)

    _____ _____ your biggest problem?

5. Tian Jun used to play football. (改为否定句)

    Tian Jun _____ _____ to play football.