氧是维持生命的必要元素。
硝酸盐中含有氮，而氮是维持生命的必要元素。
Nitrates are compounds that contain nitrogen, an element essential for life.
2005年，“卡西尼”太空探测器飞越土卫二时的勘测资料显示其表面存在碳、氢、氮、氧等元素——这些有机分子被认为是生命形成的必要条件。
Observations from the Cassini probe's 2005 flyby of Enceladus suggest the presence of carbon, hydrogen, nitrogen and oxygen - organic molecules thought to be necessary to develop life.
“也许砷并非生命生存的必要元素，但它可能是一种可接受的元素，”她补充道。
"Perhaps arsenic is not an essential component for habitability or for life, but it may be one that can be tolerated," she added.
天文学家无法断定土卫六的大气层中是否含有生命存在的必要元素。
Astronomers were not sure if Titan's atmosphere contained the elements necessary for life.
天文学家无法断定土卫六的大气层中是否含有生命存在的必要元素。
Astronomers were not sure if Titan's atmosphere contained the elements necessary for life.
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