Home Heating
Central heating became popular only afterthe Civil War. Typically, coal-burning furnaces （火炉）fueled the early systems. Natural gas had developed into the leading fuel by 1960.Its acceptance resulted in part from its wide uses.Because it comes primarily fromU.S. and Canadian fields, natural gas is also less vulnerable （脆弱的） than oil is to war. Oil remains the most important fuel in a few areas,such as New Englard.
Electric heating dominates most areas withmild winters and cheap electricity,including the South and the Northwest. It wasmade popular at least in the South by the low cost of adding electric heating tonew houses built with air-cbnditioning.Bottled gas,which is somewhat more expensivethan utility gas, is the fuel of choice in rural areas notserved by utility pipelines.Wood is the leading heating fuel in just a few rural counties.Home heating, whichaccounts for less than 7 percent of all energy consumed in the U.S., has had a commendable（值得赞扬的） efficiency record: from 1978 to 1997, theamount of fuel consumed for this purpose declined 44 percent despite a 33 percentincrease in the number of housing units and an increase in house size. The U. S.Departmentof Energy, however, forecasts that energy used in home heating will rise by 14 percentover the next two decades. That rise is small considering an expected 21percentincrease in the number of houses and the trend toward larger houses.
Natural gas end electricity will probablydominate the home heating market for the next two decades. Solar （太阳的） heating never became popular because of cost and limited winter sunlightin most areas; in 2000 only 47, 000 homes relied on it.
第 36 题 Natural gas didn't become the leading fueluntil.

A. 1978.
B. 1960.
C. 1997.
D. 2000.