A．Happiness could be produced．
B．Happiness is human's birthright．
C．Happiness can be copied．
D．Happiness is infectious．

A．TV shows．
B．Comedies．
C．Clowns．
D．Practical jokes．

A．To enrich the forms of art．
B．To prevent people from being too sad．
C．To relax the audience during tense moments．
D．To give people a little surprise．