I failed in the job interview and only then the importance of learning English well. A.

问题补充：

I failed in the job interview and only then the importance of learning English well.

A. I realized

B. I had realized

C. did I realize

D. had I realized

答案：

A. I realized

B. I had realized

(答案→)C. did I realize

D. had I realized

解析：考查only的倒装句；only的倒装句有两个条件：only放在句首；且强调状语；在这种情况下使用部分倒装句。本题only放在句首，强调的是时间状语then，故使用部分倒装的形式。句意我没有通过面试，直到那时我才意识到学好英语的重要性。故C正确。