He realized his mistakes and took action to reduce the loss it was too late. A. untilB.

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：句意：在还来得及之前，他意识到了自己的错误并采取行动减少损失。Until表示“直到------才------”，when表示“当-----时候”，as表示“当-----时候”，before表示“在------之前”。故选C。