矿井发生突水后，为了进行治水复矿，必须进行不间断的水文地质观测试验和（）工作。
A、排查
B、封堵
C、分析
D、以上都不对
参考答案：C
(2分)已知Na与H2O发生反应：2Na +2H2O ="2NaOH" +H2↑，则4.6gNa溶于_______ g H2O中才能使溶液中Na+与H2O个数之比为1：10。
— What did the doctor say about your mother's illness?
— He suggested that she _ an operation at once. [ ]
A. must have
B. had
C. have
D. has
