Only after they had discussed the matter for a few hours a decision.
A. they reached
B. did they reach
C. they reach
D. do they reach
网友回答
A. they reached
(答案→)B. did they reach
C. they reach
D. do they reach
解析：考查倒装。Only+时间状语或从句，放句首时，主句用部分倒装，A、C没倒装，排除A、C；根据had discussed可知，空白处使用过去时，排除D。故选B。