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1·Water is necessary for life.

水是生命所必需的。youdao

2·Hard work is necessary for success.

努力工作是成功的必要条件。youdao

3·A healthy diet is necessary to stay healthy.

健康的饮食是保持健康所必需的。youdao

4·Learning new skills is necessary.

学习新技能是有必要的。youdao

5·Good communication is necessary to build friendship.

良好的沟通是建立友谊的必要因素。youdao

6·Patience is a necessary quality for this job.

耐心是做好这项工作的必备品质。youdao

7·It's necessary to bring some necessities when traveling.

旅行时带些必需品是必须的。youdao

8·Proper rest is necessary for physical recovery.

适当的休息对身体恢复是必要的。youdao

9·A positive attitude is necessary to face challenges.

积极的心态是面对挑战的必要条件。youdao

10·Enough sleep is necessary for our health.

足够的睡眠对我们的健康是必不可少的。youdao

必要

1·Military action may become necessary.

军事行动可能会成为必要。《柯林斯英汉双解大词典》

2·She searched her desk for the necessary information.

她在她的书桌里搜寻必要的资料。《柯林斯英汉双解大词典》

3·We will take the necessary steps, she said sternly.

“我们将采取必要措施，”她严厉地说道。《柯林斯英汉双解大词典》

4·We are still looking for someone who combines all the necessary qualities.

我们仍在寻觅兼备所有必要才能的人选。《牛津词典》

5·They are not afraid to tackle the issues or let the sparks fly when necessary.

他们不怕应付这些问题, 必要时也不惜进行唇枪舌剑的激烈争论。《柯林斯英汉双解大词典》

需要的

1·Some adjustment of the lens may be necessary.

可能需要调整一下镜头。《牛津词典》

2·An objective set of rules which we all agree to accept is necessary for any ordered society.

任何井然有序的社会都需要一套客观公正、为大家所接受的规则。《柯林斯英汉双解大词典》

3·Earwax removal is sometimes necessary.

有时需要清除耳垢。

4·With any container that you choose, you need to ensure that it allows the water in it to drain when necessary.

对于您选择的任何容器，您需要确保在需要的时候它能够排除里面的水。

5·In areas where the wind dies down, backup electricity from a utility company or from an energy storage system becomes necessary.

在风能不稳定的一些地区，需要供电事业公司或者能量储存系统来提供备用电能。

必须的

1·Some forethought and preparation is necessary before you embark on the project.

你着手进行这个项目之前必须有所考虑，有所准备。《牛津词典》

2·They are only doing what is necessary to prevent wholesale destruction of vegetation.

他们只是在做为防止植被遭大规模破坏而必须做的事情。《柯林斯英汉双解大词典》

3·Some immediate action was necessary—but what?

必须立即采取行动——但应该采取什么行动呢？

4·Constant vigilance is necessary in order to avoid accidents.

为了避免意外事故，必须经常保持警惕。《新英汉大辞典》

5·It is necessary that a critic develop a sensibility informed by familiarity with the history of art and aesthetic theory.

批评家必须在熟悉艺术史和美学理论的基础上培养一种感性。

必需的

1·They've been deprived of the fuel necessary to heat their homes.

他们无法得到住房取暖必需的燃料。《柯林斯英汉双解大词典》

2·Reorganization is necessary on the distributive side of this industry.

此行业的产品分配环节必需重组。《柯林斯英汉双解大词典》

3·Too many people had too little patience for the grunt work necessary for long-term success.

太多的人都没有耐性为以后的成功去做眼下必需的苦差事。《柯林斯英汉双解大词典》

4·I think, maybe that was necessary because it's an important relationship.

我认为，可能那是必需的，因为这层关系太重要了。

5·These software objects would contain all the necessary business rules and would understand the business processes that should be followed.

这些软件对象将包含所有必需的业务规则，并且理解应该遵循的业务流程。

有必要的

1·If necessary I can come at once.

如果有必要，我可以马上来。《牛津词典》

2·It has been found necessary to make some cuts in the text.

已发现有必要对文章作些删节。《柯林斯英汉双解大词典》

3·It is necessary initially to classify the headaches into certain types.

起初把头疼分成若干类别是有必要的。《柯林斯英汉双解大词典》

4·I may look like a tenderfoot, but I think I can follow a trail or carry a pack if necessary.

我也许看起来像个新手，不过有必要的话我认为我也能跟着上路或扛包。《柯林斯英汉双解大词典》

5·Is advertisement really necessary?

广告真的有必要吗？

必然的

1·This is a necessary consequence of progress.

这是发展的必然后果。《牛津词典》

2·It is not, in principle, necessary for a biological system to age and die.

原则上来说，生物系统的衰老和死亡都不是必然的。

3·At the very least, it has awoken us from our national fever dream of easy riches and bigger houses, and put a necessary end to an era of reckless personal spending.

至少，它让我们从轻易致富和拥有更大房子的狂热梦想中醒来，并为一个不计后果的个人消费时代画上了一个必然的句号。

4·I think we all agree that change is necessary but inconvenient.

我想我们都同意变更是必然的，但又是不容易处理的。

5·The first billiard ball could move without the second one moving, right, there is no necessary connection between them then.

在第二个球不动的情况下第一个球还是能动的，对吧，他们之间并没有必然的切合点。

必不可少

1·And so, while gossip may not be nice, it may have once been necessary.

所以，虽然流言蜚语可能不是好事情，但它曾经却是“必不可少“的。

2·This principle is an extension of the management principle and is necessary for effective and efficient administration of the project commitment.

该原则是管理原则的一个扩展，对于项目承担义务管理的效率和效力是必不可少的。

3·It was necessary to perform tasks on all replicated servers.

而在所有已复制服务器上执行任务是必不可少的。

4·Software architecture competence is the ability of an individual or organization to acquire, use, and sustain the skills and knowledge necessary to carry out software architecture-centric practices.

软件架构能力是个人或组织获取、使用、胜任对开展以软件架构为中心的实践来说必不可少的技能和知识。

5·This notion of business processes as components is not one that is exclusive to the technical or implementation domain. A component view of a business is also necessary for greater business agility.

这个业务流程即组件的概念不是技术或实现领域专用的，业务的组件视图对于更高的业务敏捷性也必不可少。

必备

1·Digital watt-hour meter is the necessary equipment with increasingly wide application while it is necessary realization of quantity traceability.

数字式电能表是必备设备，应用越来越广泛，实现量值溯源是非常有必要的。

2·Absentee Managers - who would not step in at all irrespective of whether the team has all the necessary skills to tackle the problem.

缺席的管理者：不管团队是否解决问题的全部必备能力，这一类管理者都不会介入。

3·Several countries, including America, Britain, China, France, Israel, Japan and Russia, are thought to possess the necessary technology.

几个国家（包括美国、英国、中国、法国、以色列、日本及俄罗斯），被认为拥有这种必备技术。

4·First though, I'll give some necessary background with a look at the internal form of class names and the field and method descriptors used by the JVM.

首先将介绍一些必备的背景信息，以使您了解类名称的内部结构及JVM所使用的字段和方法描述符。

5·The pace of modern life makes stress management a necessary skill for everyone.

现代的生活节奏使得压力控制对于每个人来说都是必备技能。

必需品

1·Lunch containers were not necessary for school kids in cities.

午餐盒对于以前在城里上学的孩子来说并非必需品。

2·The large size of the settlements made improving processing and storage of necessary food difficult.

移民点的巨大规模让优化食物必需品的加工和储存变得困难。

3·Humus is necessary for rapid decomposition of leaves by bacteria and fungi and for recycling by surface roots.

腐殖质是树叶被细菌和真菌迅速分解和根部表面循环过程的必需品。

4·And California's voters have, in ballot measures over the decades, made all money matters more complicated than necessary.

在过去的十年间，加利福尼亚的选举人采取的选举措施致使所有的借贷事件比必需品还复杂的多。

5·Anyone can make the decision to do without the necessary, to cut off cable TV, to consider doing without a car, to only buy what's absolutely necessary and to rethink what's necessary.

每个人都可以做出缩减必需品的决定：剪断有线电视，卖掉小车，只买非买不可的东西，并且重新考虑哪些东西是非买不可的。

(1)if necessary如果必要的话

(1)necessary for所必需；对…是必要的

(1)necessary condition必要条件，充分必要条件

(1)when necessary在必要的时候

(1)as necessary必要时

(1)absolutely necessary绝对必要