用所给词的适当形式填空。

1. ______ (help) us learn more about plants, we planted some seeds.

2. I'm sorry to keep you ______ (wait) for so long.

3. — Don't you forget ______ (meet) me 3 years ago here?

    — Sorry, I can't remember.

4. April 1st is April ______ (fool) Day.

5. Rose is ______ (pretty) girl in the school.

照片影像的对比度与射线对比度的比为（）.

A.感光度

B.相对感度

C.平均斜率

D.反差系数

E.宽容度