Even if you spotted something suggesting a city in space, you'd still have to figure out whether the light was artificial - alien-made, in other words - or simply reflected back from the sun.

即使你在宇宙空间里发现了些什么，你还是需要分辨这些光是否人造——外星人造的，还是说，它仅仅是反射的阳光。

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Cholecalciferol is produced by irradiation of 7-dehydrocholesterol with ultraviolet light either from the sun or from an artificial source.

胆钙化醇是7 ？脱氢胆固醇经日光或人工来源的紫外线照射而产生的。

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Cholecalciferol is produced by irradiation of 7-dehydrocholesterol with ultraviolet light either from the sun or from an artificial source.

胆钙化醇是7脱氢胆固醇经日光或人工来源的紫外线照射而产生的。

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