One of the most important features that distinguish man ____16___ animals is the ___17___ to laugh． People who have ___18___ the phenomenon have ___19____ many theories to explain human __20___． Scholars in the field of psychology, for __21_, have done research _22 the subject of ___23_ makes people laugh． But as usually happens, the experts disagree, and there is 24___ controversy in the field． _25__ people claim that human __26___ laugh at things which are 27__ to their experience． Others feel
