Definition
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necessary
Necessary means required or essential, something that must be done or is needed.
必要是指被要求或必需的事情,必须完成或需要的东西。
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It is necessary to wear a seatbelt while driving.
开车时系安全带是必要的。
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She found it necessary to study every day to pass the exam.
她发现每天学习是必要的,以便通过考试。
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Having a valid ID is necessary for entering the building.
进入大楼必须持有有效的身份证件。