The pilot told us that everything was now Ok.Only then___how

The pilot told us that everything was now Ok.Only then___how dangerous the situation had been.
A.I realized
B.I had realized
C.did I realized
D.had I realized
C选项打错了.....是Had I realize,T-T

选D
only +状语 主句倒装.
then 是时间副词做状语.
所以要倒装.
C realize 用原型,故错.
其他不是倒装.
C had I realize 肯定错啊.
had 后面 是 过去分词.原型 肯定 错了.
再问： 我把C打错了，是realize
再答： 那就选C only then did I realize············ 因为 situation 危险是 在你知道之前，所以他用了 过去完成时。 但是你意识到这个 是过去。 所以 选C 而不选D