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"Geothermal (地热的) " power is based on the heat that comes from deep inside the earth. "Geo" means Earth and "thermal" means "heat". Earth's core, deep in the center of the planet, is about as hot as the sun's surface, and is expected to stay that way for billions of years. This heat slowly makes its way outward from the core. In some places, where the rocks have lots of holes in them, this heat comes out in different kinds of hot springs, with hot water and steam coming out naturally through the earth's surface. In areas like this, humans have been using the earth's heat for different purposes for hundreds of years.

In general, though geothermal energy requires drilling (钻孔) deep into the earth. There are many different ways of collecting the heat and different ways of using it. But these geothermal wells can easily produce huge amounts of heat and electricity for hundreds of years — all without pollution.

There is another positive side to geothermal energy — it can produce power day and night all year long. Solar power depends on the sun, and wind power depends on wind. That means that they are not constant. But energy from geothermal sources is always available (可获得的) . However, geothermal energy also faces a big challenge — drilling down deep enough to create a geothermal plant is hard, and it costs a lot of money. Some geothermal plants require drilling down more than 4 miles (6.5 kilometers) below the earth's surface. Drilling down even deeper can lead to much more heat and far more powerful energy sources.

The costs of all this drilling are a big part of what has limited geothermal projects. But now people are starting to think about a clever idea that could make geothermal energy far cheaper: using oil wells that are already there.

If given a mechanical (机械的) job to do, he would be set to work eagerly. When he was twelve, he became almost uncontrollably interested in clocks and watches. Soon he was repairing clocks and watches for friends.

In 1876, his wife died in childbirth. Henry suffered a blow and decided to get away from the farm as soon as he could. Three years later, he worked as a mechanic in Detroit. One day in 1877, when he first saw a steam-driven locomotive (蒸汽机车), Henry went to the locomotive driver and asked him plenty of questions about the engine's performance. From then on, Henry became crazy about steam engines. Later, with the help of an old co-worker, Henry got an engineer position at the Edison Detroit Electricity Company.

Although Henry quickly became chief engineer at the Detroit power factory, his interest in fuel engines took up his life. He spent most of his spare time trying to build an engine according to his own design. Henry went through the hard way to build an engine by hand from the beginning. It was two years before he succeeded in building a working car. It was unattractive-looking on bicycle wheels and driven by a rubber belt that connected the engine. Henry called it the "Quadricycle (四轮自行车)".

—Sorry, you mustn't. It has been taken already.

—It                    be her. She has gone abroad.