根据句意，用括号内所给词的适当形式填空。

1. My mother goes to Beijing _____ (two) a year.

2. Can you find the_____ (different) between this box and that box?

3. I _____ (hard) ever see him now.

4. Do you want to meet that _____ (interview)?

5. You should look after your _____  (healthy).

气缸的冷却水均由（）

A、下进上出

B、下进下出

C、上进上出

D、上进下出