我们可以通过控制离心泵的（）来控制流量。
A、出口阀
B、入口阀
C、止回阀
D、过滤器
参考答案：A, B
线圈的电抗的表达式是（）。
A.ωL
B.2πωL
C.2πfL
D.A和C
When his dad died, he felt his world had turned upside - down. [ ]
A. in case
B. as if
C. so that
D. even though
