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

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：句意；我工作面试时失败了，直到那时我才意识到学英语的重要性。因为前面用failed，所以这里也用过去式。在and后的分句中，only then放在句首句子应用部分到装。故选C。