The ability of coal to release a combustible gas has long been known.

煤能够释放易燃气体这一点早已为人所知。

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It has long been known that the level of serum iron in animals falls during infection.

人们早就知道，在感染期间，动物的血清铁水平会下降。

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It has long been known that the human skeleton constantly constructs and destroys cells, according to the stresses that its bones experience.

长久以来，人类骨骼被认为是依照其骨质经受的压力来不断构建和消灭细胞。

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Now, this has been known for a long time.

这一事实早已被世人所知

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Jeter has long been known for his ability to rack up 200-hit seasons, the hallmark of any 3, 000-hit campaign.

WSJ: Robinson Cano: 1,501 Hits Down, 1,499 to Go

In particular, Oracle has long been known as a category killer that ruthlessly runs smaller competitors out of business.

FORBES: Big Writedowns And Larry Ellison Are Enough Reasons To Sell Ariba

It has long been known that vitamin D prevents rickets and children were once given food supplements like cod liver oil.

BBC: Experts review vitamin D advice