题目

阅读理解 Solar energy systems/power plants do not produce airpollution, water pollution, or greenhouse gases. Using solar energy can have apositive, indirect effect on the environment, when solar energy replaces orreduces the use of other energy sources that have larger effects on theenvironment. However, some poisonous materials and chemicals are used tomake the photovoltaic (光电池的) cells that convert sunlight into electricity. Some solarthermal (保热的)systems use potentially hazardous liquids to transfer heat. Leaks ofthese materials could be harmful to the environment. U. S. 实验测得某物质中只含有碳元素，则这种物质(  ) A．一定是金刚石或石墨中的一种 B．可能是一种碳单质，也可能是几种碳单质组成的混合物 C．一定是碳元素的单质 D．一定是金刚石、石墨和C60组成的混合物