用所给词的适当形式填空.

1. The polar bears are kind of        (aggress).

2. He was____    (surprise) to find no one in the zoo.

3. Zoos are like          (live) textbooks for young people.

4. He ________(use) to be a teacher.

5. How much do you           (weight)?

肽链延伸包括：进位、______和______。