Learner's definition of OR
1
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used to introduce another choice or possibility或，或者，还是（用于引出另一个选择或可能性） -
You can have coffee or tea.你可以喝咖啡或是茶。
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Would you like beer, wine, or something else?你想喝啤酒、葡萄酒，还是其他什么？
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He must be her brother—or is he? [=maybe he is not her brother]他肯定是她的哥哥——或者不是？
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I'll call (either) today or tomorrow.我会在今天或明天打电话。
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(somewhat informal) I didn't mean to annoy you or anything.我没想惹你生气，也没其他意思。
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(somewhat informal) Can I get you a cup of coffee or something?我能给你来杯咖啡或是其他饮料吗？
2
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used in negative statements to introduce something else that is also true也不（用于否定句，引出另外一件同样真实的事情） -
We couldn't stop or even slow down the whole time. [=we could not stop and we could not slow down]我们在整段时间中不能停下，甚至也不能减速。
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They have no food or water. [=they do not have food and they do not have water]他们既没有食物也没有水。
3
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used to say what will happen if a specified thing is not done否则，要不（表示如果不做某事会引起的后果） -
Finish your dinner or you won't get any dessert. [=if you do not finish your dinner, then you will not get any dessert]把晚饭吃完，否则就不给你吃甜品。
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Be at the station by 5 o'clock or you will miss the bus.*5点钟前到达车站，不然你就赶不上公共汽车了。
4
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used to introduce another number or amount that is possibly the correct one或，或者（用于引出另一个可能正确的数字或数量） -
It's been two or three years since I've seen her.我已经有两三年没见到她了。
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The package should arrive in five or six days.包裹应该五六天后到达。
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We waited for an hour or more.我们等了有一个小时或更久。
5
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used to introduce the reason why something said previously is true否则，不然（用于引出前述事情为真的原因） 6
a —
used to introduce a word or phrase that defines or explains what another word or phrase means或者说，也就是（用于引出某一词语或短语的解释） -
Botany, or the science of plants, is a fascinating subject. = The science of plants, or botany, is a fascinating subject.植物学，也就是研究植物的科学，是一门迷人的学科。
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This pan is used for sautéing, or frying, the vegetables.这种锅是用来炒或者说油煎蔬菜的。
b —
used to introduce a word or phrase that corrects or states more precisely something you have just said或者说（用于引出更精确的描述） -
We got here quickly—or more quickly than last time, anyway. = We got here quickly—or at least more quickly than last time.我们很快就到这儿了——或者说至少比上次快。
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The building is 500, or to be precise, 502 years old.这栋大楼已有500年的历史了，或者更精确地说，是502年。
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She breeds rabbits, or rather hares.她饲养兔子，或者更准确地说，是饲养野兔。