It remains doubtful immediate measures could be taken to prevent underground water pollution.
A. how
B. whether
C. that
D. where
网友回答
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。