...because, before, if, so, so that, until, when, while的用法与区别...答:There was a loud knock at the door when he was just falling asleep.while表示的时间是一段,而不是一点,如:While he was having supper, he heard someone knock at the door.while有时还有对比的含义,如:While I was reading, he was writing.2.原因状语从句(1)常由because, since, ...