问题详情

In 1983, when oil prices were still high in my area, I installed a ground-source heat pump in my brand-new, well-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 m 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 bearings 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 prices 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.
The passage suggests that the author"s heat-pump system absorbs heat from ______
A．soil in a nearby field
B．sun panels at ground level
C．a pipe buried next to the walls
D．a tank of propylene-glycol