－How was your final exam, Tom?
－I’m sorry, dad. I failed and only then the importance of studies.
A. I realized
B. I had realized
C. had I realized
D. did I realize
网友回答
A. I realized
B. I had realized
C. had I realized
(答案→)D. did I realize
解析：考查Only的倒装句。Only放在句首，强调状语的时候，后面使用倒装句的语序。本题的only放在句首，强调的是then.故D正确。