Critics say there may be unknown risks.

评论家称，可能存在未知的风险。

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And a vast amount of data is stored in the cloud, on servers whose location may be unknown.

相当大量的数据存储在云中心，服务器的地址不详。

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The researchers think there may be unknown compounds in coffee that protect against the disease.

研究人员认为，咖啡中可能有不明物质抵御疾病。

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Some uses of data may be unknown today, but important decades hence.

FORBES: The Truth About Risks, Benefits of the Smart Grid

Mr Hague may be unknown but he is not vague.

ECONOMIST: Don��t be vague

Dr White thinks there may be an unknown one that varies on roughly the same timescale as the more regular solar cycle, and thus tends to fall into step with it, amplifying the solar variation.

ECONOMIST: The earth��s climate