Which of the following measures can help you sleep better

A．people should go to a doctor and have their problems diagnosed
B．people should exercise immediately before going to bed every night
C．people should sacrifice other things to get enough sleep if necessary.
D．People should give up going to bed and going up at the same every day.

A．Most people need less sleep when grow older.
B．Most people need seven and a half hours of sleep every night.
C．On average, people in the U. S. today sleep less per night than they used to.
D．For most people, less than six hours of sleep on a typical work night is enough.