Only when 1 was fourteenthe importance of studyA. I realizedB. did I realizeC. had I real

问题补充：

Only when 1 was fourteenthe importance of study．

A. I realized

B. did I realize

C. had I realized

D. I had realized

答案：

A. I realized

B. did I realize

C. had I realized

D. I had realized

解析：

句意：只有当我14岁时，我才意识到学习的重要性。Only修饰状语when位于句首时需使用部分倒装，本句的时态应使用一般过去式。