当泵的转速不变时，离心泵的叶轮直径和流量之间的近似关系为（）。
A.Q’/Q=D1/D2
B.Q’/Q=D2/D1
C.Q’/Q=2D1/D2
参考答案：A
You'd better ____ how much the trip will cost to see if we are able to pay for it. [ ]
A. sort out
B. add up
C. figure out
D. come up
软件是一种（）的产品。
A.物质
B.消耗
C.有形
D.辑
