圆管层流的流速是如何分布的（）？
A.直线分布
B.抛物线分布
C.对数曲线分布
D.双曲线分布
参考答案：B
解析：参看层流运动一节。
If you _______ me with my English, I will appreciate ________
A．help, your help
B．will help, your help
C．help, you
D．will help, you
The shirt is so expensive. Can you reduce the price ________a third?
A．to
B．by
C．of
D．at
