目前有几种正在研究中，比如电力引擎、燃气轮机、蒸汽机等。
There are several possibilities being researched at present, such as electric, gas turbine, and "steam" engines.
车轮和螺丝的发明，蒸汽机的问世，电力的使用，所有这些都曾改变了亿万人的生活；
The invention of the wheel and screw, the introduction of steam-power, the use of electricity, all these have changed the lives of millions;
过去的许多繁荣都是基于能量反馈的：煤炭驱动的蒸汽机，石油驱动的内燃机，电力的崛起，甚至喷气时代的大众化旅游。
Many past booms have been energy-fed: coal-fired steam power, oil-fired internal-combustion engines, the rise of electricity, even the mass tourism of the jet era.
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