Ancient Greek philosopher Aristotle viewed laughter as“a bodily exercise precious to health.”But---_____some claims to the contrary,laughing probably has little influence on physical filness Laughter does_____short-term changes in the function of the heart and its blood vessels,____heart rate and oxygen consumption But because hard laughter is difficult to____,a good laugh is unlikely to have_____benefits the way,say,walking or jogging does.____,instead of straining muscles to build them,as exercise does,laughter apparently accomplishes the____,studies dating back to the 1930’s indicate that laughter.muscles,Such bodily reaction might conceivably help____the effects of psychological stress.Anyway,the act of laughing probably does produce other types of______feedback,that improve an individual’s emotional state.______one classical theory of emotion,our feelings are partially rooted_______physical reactions.It was argued at the end of the 19th century that humans do not cry______they are sad but they become sad when te tears begin to flow.Although sadness also_______tears,evidence suggests that emotions can flow_____muscular responses.In an experiment published in 1988,social psychologist Fritz Strack of the University of würzburg in Germany asked volunteers to____a pen either with their teeth-thereby creating an artificial smile–or with their lips，which would produce a（n）_____expression.Those forced to exercise their enthusiastically to funny catoons than did those whose months were contracted in a frown，_______that expressions may influence emotions rather than just the other way around____，the physical act of laughter could improve mood.
空格所在句子是“笑?肌肉”，所选动词与muscles形成动宾关系，并且要与后半句话“decreasing muscle tone for up to 45 minutes after the guffaw subsides”语义保持一致，四个选项中[A]hardens“使变硬”，[B]weakens“使变弱”，[C]tightens“使变紧”，[D]relaxes“使松弛”，把[D]代入空中，表示笑使肌肉放松，与前一句“不像其他的锻炼可以拉紧肌肉，笑很显然起到了相反的作用”语义一致，?故[D]正
