Choose the best answer. 选择最佳答案。 Every human being, no matter what he is doing, gives off body heat. The usual problem is how to dispose of it. But the designers of the Johnstown campus of the University of Pittsburgh set themselves the opposite problem—how to collect body heat. They have designed a collection system which utilizes not only body heat, but the heat given off by such objects as light bulbs and refrigerators as well. The system works so well that no conventional fuel is needed to make the campus’ six buildings comfortable. Which of the following is true of the heating system of the Johnstown campus?