显微镜视野中出现气泡主要是制片失误的一步是（　　）

A．撕取材料

B．染色

C．擦镜

D．盖片

句型转换 

        在B 句中填入合适的词, 使之在意义上同A 句相同或相近.

1. A: "Have you ever seen him?" asked the boss.

    B: The boss asked me_______ _______ _______ ever seen him.

2. A: They seem to know what they are doing.

    B: _______ _______ _______ they know what they are doing.

3. A: Do you know the girl in our school, the parents of whom are English?

    B: Do you know the girl in our school _______ parents are English?

4. A: In the terrible earthquake, many people asked the government for help.

    B: In the terrible earthquake, many people _______ _______ the government _______help.