单项选择题
A．listened to sad music B．listened to pop music C．listened to different programs D．listened to a funny program
A．to give better condition to their patients B．to improve patients' health C．to make patients smile D．to prove smile and laughter lave the same effect
A．smiling does good to health B．laughter can produce pain C．there is a way to reduce pain D．laughter can work the muscles in the feet