Only when the firefighters put off the fire what great damage it caused.
A. we had realized
B. had we realized
C. we realize
D. did we realize
网友回答
A. we had realized
B. had we realized
C. we realize
(答案→)D. did we realize
解析：句意：当消防队员扑灭火的时候我们才意识到这场大火引起这么大的灾难。这里是倒装，only+状语放在句首时主句的谓语动词用部分倒装，，又因为从句用的是过去式，故主句用一般过去式，故选D。