单项选择题
A．refrigerated food item may go bad B．traffic lights do not work C．people must rely on candlelight D．elevators and escalators do not function
A．1,000. B．800. C．200. D．120.
A．To warn the reader to stay away from them. B．To compare their voltage to that used in houses. C．To give an example of a living electrical generator. D．To describe a new source of electrical power.