In 1983, when oil process were till high in my area, I installed a ground-source heat pump in my brand-new, and insulated 1,600-

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问题   In 1983, when oil process were till high in my area, I installed a ground-source heat pump in my brand-new, and insulated 1,600-square-foot house. It cost several thousand dollars more than comparable systems that use oil, gas, or wood, but I figured I’ d recover my higher initial expense in a few years through lower energy bills.
   True, my heat pump runs on electricity-an expensive commodity where I live. But most of its energy comes from the earth: a propylene-glycol solution circulates through 1,200 feet of two-inch-diameter plastic pipe buried three feet deep in a field next to my house. As it travels, the solution absorbs heat from the surrounding soil, even when soil temperature drops below freezing.
   My ground-source heat pump also offers important benefits that have nothing to do with economics.
   -Minimal fire hazard-no chimney, firebox, or heating elements-only pumps, fans, and a compressor.
   -Cleanliness-no combustion products, thus no chance of my heating system polluting the indoor air, leaving scummy deposits on walls and furniture.
   -Reliability-solid-state electronic controls and sealed beatings almost eliminate breakdowns.
   -No maintenance-no wood to cut, ashes to haul, or chimney to clean.
   -Convenience-The system runs automatically, even switching from heating to air conditioning as needed. I can simply lock the door and go away for a day, week, or month.
   Not only did I expect to start saving on energy costs immediately, but I also expected those savings to grow over the years as oil process continued to soar. Since I was wrong about oil prices, the big dollar savings I’ d hoped for haven’ t materialized. Nevertheless, I am satisfied, all things considered.
One benefit the author mentions is that the system______.

选项 A、uses no electricity
B、has a fire-safety shutoff
C、does not pollute the air in the house
D、pollute the air in house

答案C

解析 本题询问系统的优点,文中列举了5个优点,并有记号一一标出。与原文相比可知,只有C是属于优点之—的。
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