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that is needed for a purpose or a reason 必需的；必要的 - necessary to do something
It may be necessary to buy a new one. 也许有必要买个新的了。 - necessary for somebody to do something
It doesn't seem necessary for us to meet. 我们似乎没必要见面。 - necessary for something
Food is necessary for survival. 食物是生存所必需的。 I'll make the necessary arrangements. 我会做一些必要的安排。 Radical change was a necessary step for reform. 彻底的变革是改革的必要步骤。 - if necessary
If necessary, you can contact me at home. 必要的话，我在家时你也可以和我联系。 - when necessary
Only use your car when absolutely necessary. 非用不可的时候才用你的汽车。 - where necessary
Changes can easily be made where necessary. 必要时可以很容易地进行更改。 He has the expertise necessary to make it work. 他有必要的专业知识使其发挥作用。 I was determined not to stay in hospital for any longer than was strictly necessary. 我决定， 除非极为必要， 否则决不在医院多呆一天。
Extra ExamplesShe has the qualities necessary to be a successful teacher. 她具备成为一名成功教师所必需的素质。 The owner failed to take the steps necessary to ensure the residents' safety. 业主未能采取必要措施确保居民的安全。 Make any alterations you consider necessary. 你认为有必要的都可以修改。 The cold weather has made it necessary to protect the crops. 天气寒冷，庄稼必须加以保护。 These measures will be enforced, if necessary, by the army. 如果必要，军队会强制执行这些措施。 We are here to give help and support when necessary. 如有需要，我们随时提供帮助和支援。 You may find it necessary to readjust the wheels from time to time. 你可能会发现不时调整轮子很有必要。 qualifications which are necessary for work with the under-fives 照顾 5 岁以下儿童必需的资格
Oxford Collocations Dictionaryverbs- appear
- be
- prove
- …
- really
- strictly
- absolutely
- …
- for
- if necessary
- as necessary
- when necessary
- …
- necessary to do something
- [only before noun]
that must exist or happen and cannot be avoided 必然的；无法避免的 This is a necessary consequence of progress. 这是事情发展的必然后果。 A necessary condition for a steep fall in demand is a widespread collapse in confidence. 要使需求陡降，一个必要条件是人们普遍丧失信心。
Word Originlate Middle English: from Latin necessarius, from necesse ‘be needful’.
Idioms
a necessary evil
a thing that is bad or that you do not like but that you must accept for a particular reason 无法避免的坏事；不得已的事 The loss of jobs is regarded as a necessary evil in the fight against inflation. 失业被认为是与通货膨胀斗争中的一个必然的祸害。