计算电泵的泵效等于泵的有用功与（）的功率比值。
A、泵筒
B、电泵
C、泵轴
D、活塞
参考答案：C
______ the teacher has given permission, ______allowed to use the equipment in the lab.
A．Only if, are the students
B．If only, the students are
C．If only, are the students
D．Only if the students are
货币政策失误是导致金融动荡的根本原因，持有此观点的学者是（）。
A、弗里德曼
B、托宾
C、金德尔伯格
D、克鲁格曼
