精选优质文档-倾情为你奉上2014考研英语阅读专项冲刺练习及答案(十)The use of heat pumps has been held back largely by skepticism about advertisers claims that heat pumps can provide as many as two units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation.Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure
