According to the author, many sleeping disorders are caused by ______.

A．sleep for at least eight hours per night
B．believe that we need less sleep as we age
C．adjust our activities to the new inventions
D．be able to predict the rhythms of our biological docks

A．at about twenty-five
B．in their early fifties
C．as soon as possible after they were fifteen
D．at any age from fifteen to forty five