三、根据是否具有伴随变化来区分
若要表示主句动作伴随从句动作同时发展变化,有类似汉语“随着”的意思,英语习惯上要用as,而不用when或while。如:
The room grew colder as the fire burnt down. 随着炉火逐渐减弱,房间越来越冷。
As time goes by my memory seems to get worse. 随着时间的流逝,我的记忆力似乎越来越差。
注:若不是引导从句,而是引出一个短语,则用with,不用as。如:
With winter coming on, it’s time to buy warm clothes. 随着冬天到来,该买暖和衣裳了。
The shadows lengthened with the approach of sunset. 随着太阳下落,影子也逐渐伸长。
四、根据从句动作的规律性来区分
若暗示一种规律性,表示“每当……的时候”,英语一般要用when。如:
It’s cold when it snows. 下雪时天冷(from www.nmet168.com)。
He smiles when you praise him. 你夸奖他时他总是笑笑。
五、根据主从句动作的先后顺序来区分
若主句与从句所表示的动作不是同时发生,而是有先后顺序时,一般要用when。如:
When he arrives he’ll tell us all about the match. 等他到了,他会好好给我们讲讲那场比赛的情况。
When she had finished she waited as though for a reply. 她讲完之后等了等,仿佛是在等候回答似的。
六、根据是否具有“趁机”意味来区分
1. 若从句所表示的“当……的时候”具有“趁机”的意味,则通常用while。如:
Strike while the iron is hot. 趁热打铁。
I tried to slip the note to him while the teacher wasn’t looking. 我想趁老师不注意时把条子偷偷递给他。
有时也用when。如(from www.nmet168.com):
He stole the money when no one was by. 他趁旁边无人时把钱偷走了。
The boy looks at her repeatedly when she’s not looking. 那男孩趁她没看他的时候不断地盯着她看。
七、根据是否用作并列连词来区分
when可用作并列连词,表示“这时(突然)”;while也可以用作并列连词,表示“而”“却”(表示对比);但as则没有类似用法。如:
I was just about to go to bed when I heard a knock on the door. 我正要睡觉,听见有人敲门。
One person may like to spend his vacation at the seashore, while another may prefer the mountains. 一个人会喜欢在海滨度假,而另一个人会喜欢在山里度假。
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