Only when they were put in prison and lost freedom(自由) its importance.
A. they realized
B. did they realize
C. realized they
D. had they realized
网友回答
A. they realized
(答案→)B. did they realize
C. realized they
D. had they realized
解析：考察only的倒装句和时态。Only倒装有两个条件。当only放在句首，且强调状语的时候，后面的主句使用部分倒装的形式。本题恰好符合这两个条件。句意：只有当他们坐牢失去自由的时候，才意识到自由的重要性。不存在过去完成时的结构。故B正确。