【单选题】

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 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 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、
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