It remains to be seen this plan is practical enough to keep the project going.
A. whether
B. how
C. where
D. when
网友回答
(答案→)A. whether
B. how
C. where
D. when
解析：A 考察名词性从句。句意：这个计划是否足够可行让这个工程继续下去还有待于进一步观察。What引导主语从句，it是形式主语，根据句中的remains to be seen可知此处是指一种不确定性。故A正确。