数据保护手段中，拷贝方式存在哪些弊端？（）

A.不支持以增量方式进行数据保护

B.数据格式发生变化，不能快速使用

C.不能有效保护已经打开的文件

D.不能有效保护注册表等系统文件

句型转换,每空一词.

1. Watch TV after school. (改为否定句)

    _____ TV after school.

2. Do you have to go to bed by ten o'clock? (作肯定回答)

    _____, I _____．

3. I have to clean my room. (改为一般疑问句)

    _____ you _____ to clean your room?

4.  I have to do  my homework at home. (就画线部分提问)

     _____ you _____ to do at home?

5. Can we eat in the classrooms? (作否定回答)

    _____, you _____．