A、It distinguishes happy men from others. B、It is a luxury enjoyed by few. C、It is a unifying power. D、It serves as a daily nece

Biologically, there is only one quality which distinguishes us from animals: the ability to laugh. And it is a luxury-, for unlike any other bodily process, laughter does not seem to serve a biologically useful purpose.  In a divided world, laughter is a unifying force.  Human beings oppose each other on a great many issues, but we all share the ability to laugh.  And laughter, in turn, depends on that most complex and subtle of all human qualities : a sense of humor.  This can best be seen from the world-wide popularity of Charlie Chaplin’s early films.  The little man at odds with society never fails to amuse no matter which country we come from.  Dr.  Samuel Johnson, a great commentator on human affairs, once remarked, " Men have been wise in very different modes; but they have always laughed in the same way.
    A sense of humor and laughter may take various forms, but the effect is always the same.  The sense of humor must be singled out as man’s most important quality because it is associated with laughter.  And laughter, in turn, is associated with happiness.  Courage, determination, initiative--these are qualities we share with other forms of life.  But the sense of humor is uniquely human.  If happiness is one of the great goals of life, then it is the sense of humor that provides the key.
29. How does the speaker evaluate laughter in a divided world?
30.What does the world-wide popularity of Charlie Chaplin’s early films illustrate?
31.What opinion is stressed in the end of the passage?