Our bodies experience an ebb and flow of energy throughout the day. This is called a circadian rhythm, and it has been studied【C1】________by scientists. Our energy level builds gradually to a peak, then【C2】________, reaching a trough (低谷) about 12 hours later.    The exact nature of this cycle varies from person to person, and【C3】________do our preferences for activity versus rest.    Our natural rhythms are【C4】________by internal drives and external stimulation. Typically, external stimulation wins out over what our internal guide tells us. For example, when we fly across six time zones, we have to fit into a different time frame whether we like it or not. The same is true when we work the night shift. These are【C5】________examples of what most of us experience every day on the job.    So here we are, many of us working hours that are【C6】________to what our internal rhythms would prefer. Too bad. Or is it?    Some forward-looking companies are looking at internal rhythms as they【C7】________productivity and are finding that a mid-afternoon nap increases work output and【C8】________. But can naptime really fit into the American workday? While experts seem to agree that napping is a good idea, the reality of napping is probably a long shot at best.    There are lots of【C9】________for this. One is the need for predictability and standardization in the workplace, especially in companies that do business around the world. Another is the longstanding American work ethic that【C10】________total commitment from beginning to end of the workday. Napping is viewed as slacking, a real no-no for the go-getter who wants to get ahead.  

A. contrary     B. exclaimed C. extensively D. affected  E. prior    F. demands      G. so        H. impact      I. reasons   J. relate to    K. specifically L. accuracy  M. extreme     N. declines  O. appropriate

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