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's six buildings comfortable.
Some parts of most modern buildings－theaters and offices as well as classrooms are more than amply heated by people and lights and sometimes must be air-conditioned even in winter. The technique of saving heat and redistributing it is called “heat recovery.” A few modern buildings recover heat, but the University's system is the first to recover heat from some buildings and reuse it in others.
Along the way, pit has learned a great deal about some of its heat producers. The harder a student studies, the more heat his body gives off. Male students emit more heat than female students, and the larger a student, the more heat the produces. It is tempting to conclude that the hottest prospect for the Johnstown campus would be a hardworking, overweight male genius.
Until recently, body heat has caused problems because it____.（ ）
由文章开头的第二句“The usual problem is how to dispose of it”可知C项正确。
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
