Only when they came .
A. I left the office
B. did I leave the office
C. left I the office
D. I did leave the office
网友回答
A. I left the office
(答案→)B. did I leave the office
C. left I the office
D. I did leave the office
解析：考查only的部分倒装；当only放在句首，且强调状语的时候，后面的主句使用部分倒装的形式。本题的only放在了句首，强调的是时间状语从句when they came,后面的主句使用部分倒装的形式而不是全部倒装。故B正确。