问题补充：
He realized his mistakes and took action to reduce the loss it was too late.
A. until
B. when
C. before
D. as
答案：
A. until
B. when
(答案→)C. before
D. as
解析：A. until直到 B. when 当…时候C. before在…之前 D. as当…时候，作为；句意：他意识到他的错误并且及时的采取措施减少了损失，before it was too late在太晚之前，及时，故选C
