unless /ənˈlɛs/ conjunction Learner's definition of UNLESS
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used to say what will happen, be done, or be true if something else does not happen, is not done, or is not true除非；如果不 -
He will fail the course unless he gets a 90 on the exam.如果考不到90分，他这门功课就不及格。
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Unless something is done, the species will become extinct.如果不采取措施，这一物种将会灭绝。
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I won't have an operation unless surgery is absolutely necessary. [=I will only have an operation if surgery is absolutely necessary]除非绝对必要，否则我是不会做手术的。
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“Will I have to pay?” “Not unless [=only if] you want to.”“我要付钱吗？”“不用，除非你愿意付。”