Question

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

Answer 1

B

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。