题目内容：
根据以下内容回答题：When we work and also when we play，we use up energy．The energy may be physical or mental or a(1)of the two．If we set someone at a job and keep him at it continuously(2)rest，ultimately he will break(3)and be unable to go on．If，(4)，he can sloop for a while or do something else for a change，he will be able to work for a longer period of time．Efficiency，then，seems to be to some(5)a matter of the distribution of work and rest periods．In ordinary life work and rest usually take place by(6)．We work during the day，and sleep at night．We continue to(7)between work and rest year in and year out．
We notice first that the work is less efficient at the very beginning than he is after working a short time．This phenomenon，(8)“warming up，”is found in many different activities．Some activities need a long warming up period(9)others need a short period．The speed at which the point of highest efficiency is reached varies(10)individual to individual．
请回答(1)题 A．circle
B．combination
C．double
D．sequence
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