匯智英語自學(xué)課堂突破口語中級篇突破口語D lesson43

Heating and air conditioning in the states is usually done by what it called central heating and air-conditioning. A heating unit in the basement of a house burns gas to heat air or water, which is then forced through the house or building to raise its temperature. An air-conditioning unit outside the house or building runs uses electricity to cool the air and then sends into the building through openings in the rooms of the buildings. People have to pay, of course, for the electricity they use and the gas they burn to keep their homes at just the right temperature.