C.before
主句谓语动词强调动词的迟缓性,只用before,常伴有时间段状语或时间段暗示.例：
(1)It was quite some time before he found the elephant at all.
(2)We had walked a long way before we found some water.
(3)We had sailed for two days before we saw the land.
(4)The fire lasted about four hours before the firefighters could
control it.