Solar 24/7 Power after dark remains a challenge for the solar home.

Solar 24/7 家用太阳能面临的问题就是天黑以后。

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Dark energy's true nature remains a mystery. Theoretical attempts to account for its observed properties have foundered.

暗能量的真实本性仍然是个未解之谜，从理论上解释观测到的性状已经失败了。

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Even today, the truth about those dark days remains a delicate subject.

即使是今天，那些黑暗日子的真相仍然是一个微妙的话题。

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Dark matter remains a mystery because there has been no direct observation of it, he explained.

CNN: Space station detector gives first clues to 'dark matter'

Dark Souls remains one of my favorite games of all time with or without the PvP.

FORBES: Connect

But exactly what's driving that expansion - the force responsible for pulling the Universe apart, and for want of a better description, dubbed dark energy - remains a mystery.

BBC: Getting the measure of dark energy