It has been known for some time that plants use chemicals to communicate with each other.

人们很早就知道，植物使用化学物质来相互交流。

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Tea from China began to be sent abroad more than a thousand years ago and since then it has been known to the world.

来自中国的茶叶在一千多年前就开始被送往国外，从那时起它就为世界所知。

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It has been known that both animals and humans are willing to take a risk to satisfy their curiosity despite knowing that the result will remain unchanged.

众所周知，尽管知道结果不会改变，动物和人类都愿意冒险来满足好奇心。

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"When our government has information on a known extremist and that information is not shared and acted upon as it should have been and this extremist boards a plane with dangerous explosives that could cost nearly 300 lives, a systemic failure has occurred.

VOA: standard.2009.12.29

It says the discovery of the heaviest element known to science has been reported.

它说科学家们发现了最重的元素,并且已经上报了。

麻省理工公开课 - 固态化学导论课程节选

There is so much history at Sun, it has been known to reduce grown men to tears.

BBC: Music City to Dixieland: A musical roots run

It has been known for months that not all was well at the Clinton headquarters.

ECONOMIST: Hillary Clinton sacks her strategist, Mark Penn

It has been known for a long time that mutations in a protein can encourage amyloid formation.

ECONOMIST: Folding stuff