介绍： 版权归原作所有，仅供此学习，若有侵权请告知删除。
[11:55.41]The last reading.
[11:57.51]Petroleum
[11:59.12]Petroleum has been important since ancient times.
[12:03.39]The Greek historian told of its use
[12:06.27]in the form of pitch for building and road making.
[12:09.81]Petroleum is a fossil fuel.
[12:12.1...

介绍： 版权归原作所有，仅供此学习，若有侵权请告知删除。
[11:55.41]The last reading.
[11:57.51]Petroleum
[11:59.12]Petroleum has been important since ancient times.
[12:03.39]The Greek historian told of its use
[12:06.27]in the form of pitch for building and road making.
[12:09.81]Petroleum is a fossil fuel.
[12:12.19]The liquid comes from the remains of plants and animals
[12:16.30]that died millions of years ago.
[12:19.44]These remains were buried deep below levels of rock
[12:23.44]over time and under great pressure.
[12:26.83]This geological process created complex molecules of hydrogen and carbon.
[12:33.17]Oil can also contain other elements.
[12:36.82]Crude oil, or unprocessed petroleum,
[12:40.35]is called sour when it contains a lot of sulphur, an impurity.
[12:45.69]Sour crude requires more refining than sweet crude,
[12:49.89]which is low in sulphur and, as a result, often more valuable.
[12:55.05]The modern history of oil started in the middle of the 1800s.
[13:00.07]At that time, a method was found to make kerosene fuel from petroleum.
[13:06.09]This kind of fuel became popular for heating and lighting.