【题目】It is not until all the fish died in the river ________how serious the pollution was.
A.did the villagers realize
B.that the villagers realized
C.the villagers did realize
D.didn't the villagers realize

【答案】B
【解析】句意：直到河里的鱼都死光了,村民们才意识到污染是多么严重。此处是It is not until ...that...，的强调句型，所以答案是B。