开启或关闭固定消防炮阀门时应缓慢动作，防止产生（）现象，损坏部件。
A、“气击”
B、“气锤”
C、“水锤”
D、“水击
参考答案：D
已知以原点为顶点的抛物线C，焦点在x轴上，直线x-y=0与抛物线C交于A，B两点，若P(2，2)为AB的中点，则抛物线C的方程为（ ）。
— If we take a plane, we'll of course have arrived in London by the next weekend.
— Don't be too sure. We should _____ the weather factor. What shall we do if it is foggy? [ ]
A. look for
B. allow for
C. prepare for
D. wait for
