At the beginning of this century, medical scientists made an interesting discovery（发现）: we are built not just of flesh (肌肉) and blood but also of time. They were able to show that we all have a ‘body clock’        us, which controls the        and fall of our body energies. It can        us different from one day to the next.
The idea of a ‘body clock’ should not be too        because the lives of most living things are controlled by the 24-hour night-and-day cycle (循环). We feel        and fall asleep at night. We become        and energetic during the day. Most people will have a bad feeling if the 24-hour cycle is       . For example, people who are not used to working at night can find that lack (缺少) of sleep causes them to      badly at work.
       the daily cycle of sleeping and waking, we also have other cycle which lasts longer than one day. Most of us would        that we feel good on some days and not so good on others; sometimes our ideas seem to be so active and at other times, they are not.

A．beside B．inside C．outside D．under

A．life B．offer C．use D．rise

A．show B．treat C．make D．change

A．difficult B．natural C．surprising D．frightening

A．quiet B．tired C．comfortable D．cheerful

A．regular B．serious C．lively D．clear

A．disturbed B．pushed C．restarted D．troubled

A．perform B．suffer C．count D．control

A．With B．As well as C．Except D．Rather than

A．afford B．admire C．advise D．agree