比较while,when,as:
1、as, when 引导短暂性动作的.动词。例如:Just as / Just when / When I stopped mycar, a man came up to me.我刹车后,有一个人向我走来。
2、当从句的动作发生于主句动作之前,只能用when 引导这个从句,不可用as 或while。例如:Whenyou have finished your work, you may have a rest.干完活后,你可以休息一下。
3、从句表示“随时间推移”连词能用as,不用when 或while。例如: As the day went on, the weather gotworse. 日子一天天过去,天气越变越坏。