问题
选择题
Only after I read the book _______ why she devoted all her life to medical work for
Chinese women and children.
A．I understood
B．had I understood
C．did I understand
D．I had understood
答案
答案：C
考查倒装句.以only开头的句子,主句用部分倒装.句意,我读了这本书后,明白了她为什么……，可知主句表述的是过去发生的动作，故用过去时态，选C。