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．Disobedience. B．Laziness. C．Lack of intelligence. D．Vanity.
A．should be introduced, for it really works at the school where he once studied B．should not be introduced, for it may cause disturbance C．should be introduced though it may not work effectively D．needn't be introduced as long as teachers don't smoke in front of children