单项选择题
A．method of concealing the source of heat B．special form of air conditioning C．supplementary hot water system D．way of reclaiming and re—using heat
A．The heat is supplied by human bodies only. B．The heat is supplied by both human bodies and other heatemitting objects. C．The heat is supplied by both human bodies and conventional fuel. D．The heat is supplied by human bodies, other heatemitting objects, and conventional fuel.
A．if the winter is especially warm B．during all of the year except the winter C．in the winter as well as in other seasons D．during the evenings in the winter