水电站平水建筑物主要包括（）。
A.坝
B.调压室
C.隧洞
D.压力前池
E.溢洪道
参考答案：B, D
The teacher gave us so difficult a problem _____ we couldn't solve.
The teacher gave us so difficult a problem _____ we couldn't solve it. [ ]
A. as, that
B. that, as
C. which, that
D. the ones, which
用脚踩住制动踏板起动车辆，发动机着火后，感觉到踏板下沉，说明车辆（）
A.真空助力器密封状况良好
B.真空助力器使用状况良好
C.预留制动踏板余量过大
