Elections are essential for the sustenance of parliamentary democracy.

选举制度是维持议会民主所必不可少的。

《牛津词典》

So we've been talking about nutrients, the elements in the environment that are essential for living organisms to develop, live a healthy life, and reproduce.

所以我们一直在讨论营养，环境中的元素对于生物体的发展，健康的生活和繁殖是必不可少的。

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Indeed, it may be for any of the factors, physical as well as biotic, that are essential for organisms.

事实上，竞争对象可能是生命体所必须的任何生物或非生物因素。

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The mobile phone comes standard with latest versions of common applications that are essential for business.

ENGADGET: NTT DoCoMo's Fujitsu F-07C now available, marries Windows 7 and Symbian at last

It doesn't promote the critical thinking and problem-solving skills that are essential for good quality learning.

BBC: ��Pub quiz facts curriculum�� opposed

And they are buying hard assets, which right now are essential for China's development.

NPR: China's Growing Appetite for Business