在500名病例与500名对照的匹配病例对照研究中，有400名病例与100名对照具有暴露史。据此资料，计算OR值为（）

A.16

B.18

C.20

D.10

E.无法计算

用所给单词的适当形式填空。

1. Giraffes like eating the            (leaf) of trees.

2. Dogs are very            (friend) to us. They can help us a lot.

3. We want to see the koalas            (one).

4. How many            (monkey) can you see?

5. What is it? You can have three            (guess).