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

电针治疗扭挫伤首选的波型是

A．密波

B．疏波

C．疏密波

D．断续波

E．钜齿波