Only when he got there how much damage had been caused.A. be realizedB. he had realizedC.

问题补充：

Only when he got there how much damage had been caused.

A. be realized

B. he had realized

C. had he realized

D. did he realize

答案：

A. be realized

B. he had realized

C. had he realized

(答案→)D. did he realize

解析：当only置于句首，强调状语成分的时候，主句用部分倒装的形式。故选D。句意：只有当他到达了那里，他才意识到导致的损失有多大。