when：表示一件事在某一时间发生，例I came home when 7o'clock.（我七点回家。）；while：表示一件事发生时另一件事也在发生，I came home while she was watching TV.（我回家时她正在看电视。）；among：在三者(或三者以上)中，区别于between(两者中)；as soon as：一......就......Please call me as soon as you arrive at home.(请一到家就给我打电话。)。
