很明显，乙烯是水果中天然的植物激素，使水果成熟。
Ethylene is the natural plant hormone in fruit that makes them turn ripe, apparently.
其次，美国钻探石油和天然气的历史悠久，进而衍生出一个庞大的具有竞争力的石油服务行业，专业设备完善，专业技术成熟。
Second, America has a long history of drilling for oil and gas, which has spawned a huge and competitive oil-services industry bristling with equipment and know-how.
一些人预测在太阳能和风能还不成熟的时候，随着天然气发电的进步，将会出现风气和太阳能-天然气的综合发电站。
Some foresee hybrid wind-gas and solar-gas plants, with gas producing electricity when sun and wind are weak.
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