Only when the European countries’ financial system broke down to take measures to deal wit

问题补充：

Only when the European countries’ financial system broke down to take measures to deal with those problems.

A. did they decide

B. they decided

C. they had decided

D. had they decided

答案：

(答案→)A. did they decide

B. they decided

C. they had decided

D. had they decided

解析：考查倒装句。only+when引导的状语从句提前，主谓应部分倒装。排除B、C; 有根据broken down，可知应用过去时，故答案为A。