while与when以及as之间的区别。1. 当从句中的谓语动词是持续性的动作时,我们可以用while, when或as。While / When / As I was walking down the street, I noticed a police car in front of the bank.我顺着马路往前走时,发现银行门前停着一辆警车。2. 当从句中的谓语动词表示瞬间动作时,不可用while。He was on the point of leaving when someone knocked at the door. 他正要走,这时有人敲门。3. 如果谈论两个长动作,最常用的
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