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n. ��Ҫ����Ȼ�ԣ�����Ʒ

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n. essential��necessary��requirement��requisite

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n.   inessential��nonessential

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1. They have to do this test of necessity.
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2. The best teacher one can have is necessity.
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3. This is, of necessity, a brief and incomplete account.
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n.
  1. the condition of being essential or indispensable
  2. anything indispensable

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Necessity
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logical necessity
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moral necessity
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metaphysical necessity
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The necessity
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