离心泵的流量取决于泵的结构尺寸、（）和转速。
A.叶轮体积，叶片厚度
B.叶轮厚度，叶片直径
C.叶轮厚度，叶片长度
D.叶轮直径，叶片宽度
参考答案：D
Suppose the CPI basket contains only two kinds of goods (services): gasoline and taxicab service. In the base period, consumers bought 15 gallons of gasoline at $6 and 4 miles of taxicab at $3 each. In the current period, consumers buy 15 gallons of gasoline at $6.2 and 4 miles of taxicab at $2.5 each. The CPI for the current period is closest to:（）
A. 99.0.
B. 101.2.
C. 115.3.
These surveys indicate that many crimes go having been unrecorded by the police, mainly because not all victims have reported them.
A．unrecorded
B．to be unrecorded
C．have been unrecorded
D．to have been unrecorded
