Cloze Ancient Greek philosopher Aristotle viewed laughter as 'a bodily exercise precious to health.' Laughter does _ 1 _ short-term changes in cardiovascular(心血管的) function and respiration, boosting heart rate, respiratory rate and depth, as well as oxygen consumption. But because hard laughter is difficult to last, a good guffaw(loud laugh)is unlikely to have _ 2 cardiovascular benefits the way walking or jogging does. _ 3 _ , instead of building up muscles, as exercise does, laughter apparently accomplishes the _ 4 _. Studies _ 5 _ back to the 1930s indicate that laughter _ 6 _ muscles, decreasing muscle tone(肌肉紧张度) for up to 45 minutes after the guffaw subsides. Such physical relaxation might help _ 7 _ psychological stress. After all, the act of laughing probably does produce other types of physical feedback that _ 8 _ an individual's emotional state. _ 9 _ one classical theory , our feelings are partially rooted in physical reactions. American psychologist William James and Danish physiologist Carl Lange argued at the end of the 19th century that humans do not cry _ 10 they are sad but that they become sad when the tears begin to flow. Although sadness also goes before tears, evidence suggests that emotions can flow from muscular responses. In an experiment published in 1988, social psychologist Fritz Strack of the University of W? rzburg in Germany and his colleagues asked volunteers to _ 11 _ a pen either with their teeth-thereby creating an artificial smile-or with their lips, which would produce a _ 12 _ expression. Those forced to exercise their smiling muscles _ 13 _ more energetically to funny cartoons than those whose mouths were contracted in a frown(皱眉)did, suggesting that expressions may influence _ 14 _ rather than just the other way around. _ 15 _, the physical act of laughter could improve mood. (     )1. A. reflect (     )2. A. measurable (     )3. A. In turn (     )4. A. opposite (     )5. A. dating (     )6. A. hardens (     )7. A. cause (     )8. A. improve (     )9. A. Except for (     )10. A. unless (     )11. A. fetch (     )12. A. disappointed (     )13. A. adapted (     )14. A. emotions (     )15. A. Eventually B. demand B. manageable B. In fact B. impossible B. dated B. weakens B. generate B. decrease B. According to B. until B. bite B. excited B. adjust B. motions B. Consequently C. indicate C. affordable C. In addition C. average C. to date C. tightens C. relieve C. relax C. Due to C. if C. pick C. joyful C. turned C. movement C. Similarly D. produce D. renewable D. In brief D. expected D. date D. relaxes D. produce D. increase D. As for D. because D. hold D. indifferent D. reacted D. motive D. Comparatively