当knock off和knock over同时在表示“撞倒”意思的时候,knock over一般就是指撞倒（+ed被动）,比如说A boy was knocked over by a passing car but was fortunately unhurt.而knock off则指从某个地方（被）撞倒,如A boy was knocked off his bike by a passing car but was fortunately unhurt.knock off:
knock off
打翻;撞倒
撞倒;打掉
The little girl knocked the glass off by accident.小女孩不小心碰落了玻璃杯.
减去
They knocked off five dollars from the price.他们把价格降低了五美元.
停止;歇工
Let's knock off now.咱们现在歇一会儿吧.
knock over
打翻;撞倒
He knocked a glass over.他把玻璃杯打翻了.
使惊奇
She was knocked over by the news.她被那消息惊呆了.
消除
We have knocked over every difficulty.我们已排除种种困
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