It remains doubtful immediate measures could be taken to prevent underground water pollut

问题补充：

It remains doubtful immediate measures could be taken to prevent underground water pollution.

A. how

B. whether

C. that

D. where

答案：

A. how

(答案→)B. whether

C. that

D. where

解析：考查主语从句。本句中的it是形式主语，真正的主语是后面的whether immediate measures could be taken to prevent underground water pollution.因为主句的谓语部分是remains doubtful仍然很怀疑，说明是不确定的事情，故使用whether。句意：是否会有立刻的措施被采取来阻止地下水污染仍然值得怀疑。That引导的主语从句表示的是确定的事情，AD项的句意不相符。故B正确。