离心泵振动并发出较大噪声，是由于（）引起的。
A.联轴器不同心
B.泵的运转温度过低
C.电机电流不足
D.吸人管路堵塞
参考答案：A
At the sight of the snake, the little girl _____ move.
A．dares not
B．doesn’t dare to
C．dare not to
D．dares not to
It's time _________ breakfast. [ ]
A. for
B. having
C. have
D. to has
