...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, ...