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当前学科：龋病
题目：
单选
正常釉质中孔隙容积占（）
A . 0.1%
B . 1%
C . 2%～4%
D . 5%
E . 25%
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PARIS—An energy watchdog is alarmed about the threat to the environment from the soaring electricity needs of gadgets like MP3 players, mobile phones and flat screen TVs. In a report today, the Paris-based International Energy Agency estimates new electronic gadgets will triple their energy consumption by 2030 to 1 700 terawatt(太瓦)hours, the equivalent of todays home electricity consumption of the United States and Japan combined. The world would have to build around 200 new nuclear power plants just to power all the TVs, IPods, PCs and other home electronics expected to be plugged in by 2030, when the global electric bill to power them will rise to $ 200 billion a year, the IEA said. Consumer electronics is "the fastest growing area and its the area with the least amount of policies in place" to control energy efficiency, said Paul Waide, a senior policy analyst at the IEA. Electronic gadgets already account for about 15 percent of household electric consumption, a share that is rising rapidly as the number of these gadgets multiplies. Last year, the world spent $80 billion on electricity to power all these household electronics, the IEA said. Most of the increase in consumer electronics will be in developing countries, where economic growth is fastest and ownership rates of gadgets is the lowest, Waide said. "This will jeopardize efforts to increase energy security and reduce the emission of greenhouse gases," blamed for global warming, the agency said. Existing technologies could cut down gadgets energy consumption by more than 30 percent at no cost or by more than 50 percent at a small cost, the IEA estimates, meaning total greenhouse gas emissions from households electronic gadgets could be held stable at around 500 million tons of CO2 per year.The energy consumption of new electronic gadgets at present______.A．is nearly 1 700 terawatt hoursB．is nearly 600 terawatt hoursC．equals to the home electricity consumption of the United StatesD．is greater than the home electricity consumption of Japan