The cost of heating your home, particularly during the colder winter months, makes up about 60% of energy bills. If you need a new boiler (锅炉), make sure you buy one of the best boiler brands. The first question you should ask yourself if you want the most energy-efficient boiler is what type of boiler you should buy. All modern boilers that you can buy are condensing (冷凝式)boilers, which are much more efficient than traditional non-condensing boilers. According to a study, you could save as much as 340 pounds a year on your gas bill if you're trading in an oldstyle non-condensing boiler for a new condensing one. According to the passage, people pay more than half of their energy bills for _______.A. lighting and cookingB. heating their homeC. cooling their housesD. powering electric devices