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
网友回答
(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。