It was not until the subprime loan crisis（次贷危机） great damage to the American financial system that Americans the severity of the situation．
A. caused, realized
B. had caused, realized
C. caused, had realized
D. was causing, had realized
网友回答
A. caused, realized
(答案→)B. had caused, realized
C. caused, had realized
D. was causing, had realized
解析：考查时态。not until引导的状语从句，从句用过去完成时，主句用一般过去时，故选B。