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  3. Energy from Natural Gas 1. Much of the world gets its energy from fossil fuel sources, including coal, oil, and natural gas,

Energy from Natural Gas 1. Much of the world gets its energy from fossil fuel sources, including coal, oil, and natural gas,

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问题                     Energy from Natural Gas
   1. Much of the world gets its energy from fossil fuel sources, including coal, oil, and natural gas, all of which were created millions of years ago.The process began with dead plant and animal matter that collected and over time was buried deep within the earth. There, exposed to extreme pressure and temperatures, the carbon-based material underwent various chemical and physical changes. Some of it became coal, some oil, and some natural gas, depending on the exact conditions it was subjected to.
   2. Natural gas is both invisible and odorless. During the first century of the fossil fuel era, it was disregarded as a worthless byproduct of coal and oil. However, people later discovered that it could also be a useful source of energy, and they set about trying to realize its potential. Its use began to grow in the twentieth century and has increased rapidly within the last 40 years. Nowadays, natural gas is employed all over the world to heat homes, generate electricity, power factories, and even fuel vehicles.
   3. Because it was created through the same process as other fossil fuels, natural gas can often be retrieved from oil fields, something known as an associated source. Coal beds have similarly been known to yield natural gas. In addition, there are isolated deposits containing only gas that are referred to as non-associated sources. To access a subterranean natural gas pocket, a hole is drilled down into it, just as in oil extraction. However, due to the gas’s lightness, it will rise to the surface on its own instead of having to be pumped out.
   4. The compound we know as natural gas is actually a composite of several different substances, the primary one being methane gas. Each deposit has a unique makeup, but other common components of natural gas include propane, butane, and sulfur. Borrowing terms used in the description of oil, natural gas with a high sulfur content is called "sour" while that with a low content is referred to as "sweet" Regardless of the exact composition, natural gas must be refined to remove its impurities; when ready for use, it is nearly pure methane.
   5. Natural gas offers many advantages as a fuel source, the first and most important being that it is extremely clean burning. While oil and coal both have complex molecular structures, methane’s is simple: one carbon atom surrounded by four atoms of hydrogen. The lack of excess particles translates into fewer waste byproducts during combustion. For example, all fossil fuels produce carbon dioxide when burned, but natural gas releases substantially less carbon dioxide than other fuels. Given the major role of carbon dioxide in the acceleration of global warming, this is an important attribute. In addition, natural gas emits far less nitrogen and sulfur, which are key contributors to the smog that pollutes the air in metropolitan areas, as well as acid rain.
   6. The benefits of natural gas extend far beyond its cleanliness. Since it contains fewer waste particles, its energy can be acquired with much more efficiency than that of the other fossil fuels, meaning a lower overall cost for the consumer. A Another advantage is that natural gas is transported via underground pipelines instead of by ships and trucks.B  Finally, natural gas is relatively plentiful and widespread.C Geologists have identified extensive stores in Canada, the United States, Russia, the Middle East, and Australia, among other locations.D With the world’s oil supplies quickly dwindling, it is becoming more important than ever to utilize alternative energy resources such as natural gas.
   7. Of course, no energy resource is perfect, and there are some drawbacks to the use of natural gas. Its low density means that it requires larger tanks for storage than oil and coal do, and it is impossible to pipe it across the oceans. Some people have concerns about its safety as well, since its lack of color and smell can make detecting a leak difficult. However, when both its positive and negative characteristics are weighed, it becomes clear that natural gas is perhaps the best energy resource available today.
Why does the author discuss carbon dioxide’s relationship to global warming in Paragraph 5?
选项 A、To illustrate methane’s molecular structure.
B、To show the link between global warming and smog.
C、To suggest that fossil fuels should not be burned.
D、To elaborate on a benefit of natural gas’s cleanliness.
答案D
解析
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