单项选择题
A．listened to different radio programs B．could produce a kind of chemicals C．don't have stress or pain D．listened to a funny program
A．laughter and physical exercise have similar effects on the human body B．smile can produce the same effects as laughter C．pain can be reduced by laughter D．laughter is the best medicine
A．with words only B．in many different ways C．in letters and with drawings D．with smiles, tears and hands