It is a good plan in theory, but it to be seen whether it works in practice.
A. keeps
B. stays
C. stands
D. remains
网友回答
A. keeps
B. stays
C. stands
(答案→)D. remains
解析：考查固定句型：It remains to be seen whether…，是否…还有待证实，句意：在理论上这是好的计划，但是否在实际上能奏效还有待证实。Keep，stay，stand都不可以接to be。选D。