He waited ________ the volcano became quiet and he was able to return two days later.
A. when B. before C. as D. until
He waited ________ the volcano became quiet and he was able to return two days later.
A. when B. before C. as D. until
D
until引导的时间状语从句。句意为“他一直等到火山平息下来,两天后他才得以重回火山上”。