Not until the fish died in the river how serious the pollution was

Not until the fish died in the river             how serious the pollution was

A.did the villagers realize

B.the villagers realized

C.the villagers did realize

D.didn’t the villagers realize

答案及解析： A

解析：

英语中否定词在句首时句子的主语和谓语通常要部分倒装。