Question

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

Answer 1

A

考察倒装句，当only放句首时，后面的主句要用部分倒装句，即提前助动词或者情态动词，根据句子结构可知，主句的时态应当和when引导的时间状语从句的时间保持一致，所以选择A
句意为，只有当欧洲国家的经济体系崩溃的时候，他们才会决定采取措施处理这些问题。