When the star exhausts its usable fuel, it abruptly loses the constant struggle to hold up its own weight.

当恒星耗尽了可使用的燃料时，它会突然失去用以支撑它本身重量的惯有力量。

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But it requires energy to separate the algae from the water and then process the oil they make internally into a usable fuel.

但是这需要能量将藻类从水中分离出来，然后加工成可用燃料。

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The internal-combustion engine is a device used to convert the chemical energy ofthe fuel into heat energy, and then to convert this heat energy into usable mechanicalenergy.

译：内燃机是用于将燃料的化学能转化为热能，再将热能转化为可用机械能的装置。

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Until we actually have a way of turning all the natural gas in the ground into usable fuel for the economy, then this issue will persist (or so it would seem), and sadly the T.

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In Darfur, women must walk up to seven hours, three to five times a week, just to find a single tree with usable firewood to fuel their fires.

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India has since designated some of its reactors as civilian, and open to inspection, but others still churn out spent fuel richly laden with weapons-usable plutonium.

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