许多科学家都知道他。
Long ago scientists knew that current was a form of energy.
很久以前科学家就知道电流是能的一种形式。
Scientists knew it was old, but its exact date has been a matter of controversy.
科学家们知道它历史悠久，但是具体悠久到什么年代一直是个存在争议的问题。
Scientists already knew how the composition of water varies throughout the country.
科学家已经知道全国各地水的成份变化情况。
Scientists already knew how the composition of water varies throughout the country.
科学家已经知道全国各地水的成份变化情况。
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