有可能成为第1级别的学生有多少种不同的组合A．1 B．2 C．3 D．4

绿头鸭食物消化后形成的残渣，0.5小时后就随粪便排出体外，说明消化道中（　　）的结构很短．

A．小肠

B．大肠

C．直肠

D．肛门

用所给词的正确形式填空。

1. He has a lot of homework             (do).

2. I'm not sure whether I             (be) on time.

3. If we            (take) good care of the young trees, they will grow up quickly.

4. Have you read the book            (call) "Gone with the wind?"

5. We            (come) if it doesn't rain tomorrow.

6. You have to spend half an hour            (read) English every day.

7. Here            (come) the bus!

8. Is that house large enough for all of us            (live) in?

9. When school was over yesterday, it            (snow).

10. I'm too tired. Let's            (stop) to have a rest.

不同废物有不同的安全处置期要求，危险废物填埋场的安全处置期大于( )年。

A．50

B．100

C．150

D．200

关于骨盆的组成，下列哪项不确切（）

A.骶骨

B.尾骨

C.髂骨

D.坐骨

E.椎骨

油罐油品收发作业后计量，为什么要有一定的稳油时间？