电动放风阀的紧急电空阀动作后（）压力通过紧急阀进入放风阀膜板下部，使其动作。
A、列车管
B、总风
C、大气
D、弹簧
参考答案：B
A few minutes earlier, and you would have seen the NBA star. But you ______.
A．didn’t come
B．don’t come
C．haven’t come
D．won’t come
送电线路额定电压是如何规定的？
