木龙骨吊顶钉中间部分的次龙骨时，要按规定调整主龙骨的起拱高度，一般7～10m跨度的房间起拱（）。
A、1‰
B、3‰
C、5‰
D、7‰
参考答案：B
用括号内所给词的适当形式填空。
1. My brother _____ (have)a baseball.
2. _____ he _____ (play) sports every day?
3. She ______ ( not watch) TV in the evening.
4. Let's ______ (take) these books to the classroom.
5. Can you ______ ( bring) the pen to me?
6. We have many ______ ( sport) clubs.
7. He only watches ______ ( they) on TV.
8. I have only one ______ ( watch).
9. Let ______ ( I ) have a look.
10. Tom ______ ( not do) sports in the morning.
某一DNA分子含有20%的A+T，那么它转录成的信使RNA中的G+C的含量（）
A.40%
B.80%
C.60%
D.20%
