句型转换。  

1. My father is a bank clerk. (对划线部分提问) 

    _____ _____ your father _____?

2. His sister works in a restaurant. (对划线部分提问)

    _____ _____ his sister _____?

3. The boy wants to be a shop assistant. (改为一般疑问句并作肯定和否定回答)

    —_____ the boy _____ to be an actor?

    —Yes, He _____.

    —No, he _____.

4. My brother works at the police station. (改为否定句)

    My brother _____ _____ at the police station.

5. What does his father do? (改为同义句)

    _____ his _____ _____? 

    _____ _____ his father?

简述低碳钢、中碳钢和高碳钢的划分标准及其各自的性能特点。