Only when he returned the truth.
A. he found out
B. did he find out
C. he finds out
D. does he find out
网友回答
A. he found out
(答案→)B. did he find out
C. he finds out
D. does he find out
解析：考查倒转句。当only放在句首，且强调状语的时候，后面的句子使用部分倒装的形式。本题only放在句首，强调的是时间状语从句when he returned，故后面使用部分倒装的形式。根据returned说明使用过去时。故B正确。