From the text, we can infer that if one can't fall asleep, it might be because of ______.

A．Tranquillizers and sleeping pills can be used to cure insomnia.
B．Only the situational factors will affect our sleeping.
C．Stimulating drinks can force us to fall asleep.
D．We can decide how many sleeping pills to take on our own.

A．one had better do nothing but try to sleep
B．one Can cure himself by taking medicine
C．one had better see a doctor and follow the doctor's prescriptions
D．one can correct his bad habits so as to fall asleep again