单项选择题

The invention of light bulb by Thomas A. Edison in 1879 created a demand for a cheap, readily available fuel with which to generate large amounts of electric power. Coal seemed to fit the bill, and it fueled the earliest power stations (which were set up at the end of the nineteenth century by Edison himself). As more power plants were constructed throughout the country, the reliance on coal increased. Since the First World War, coal-fired power plants have accounted for about half of the electricity produced in the United States each year. In 1986 such plants had a combined generating capacity of 289,000 megawatts and consumed 83 percent of the nearly 900 million tons of coal mined in the country that year. Given the uncertainty in the future growth of nuclear power and in the supply of oil and natural gas, coal-fired power plants could well provide up to 70 percent of the electric power in the United States by the year 2010.
Yet, in spite of the fact that coal has long been a source of electricity and may remain one for many years (coal represents about 80 percent of the United States fossil-fuel reserves). It has actually never been the most desirable fossil fuel for power plants. Coal contains less energy per unit of weight than natural gas or oil, it is difficult to transport, and it is associated with a host of environmental issues, among them acid rain. Since the late 1960s problems of emission control and waste disposal have sharply reduced the appeal of coal-fired power plants.

In the author's opinion, the importance of coal-generated electricity could increase in the future for which of the following reasons（）

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