It is a good plan in theory but it remains whether it works in practice.A. seeingB. to s

问题补充：

It is a good plan in theory, but it remains whether it works in practice.

A. seeing

B. to see

C. seen

D. to be seen

答案：

A. seeing

B. to see

C. seen

(答案→)D. to be seen

解析：考查remain的用法：句意：这在理论上是个好计划，但是在实践中是否奏效还有待证实。Remain后面接不定式，表示“仍然要做…”，因为it和see是被动关系，用不定式的被动式，选D。