依据Unit2 课文填空: A fad 1)( ) a very short time and is not very 2)( ) . A social trend, however, 3)( ) a long time and becomes a true part of modern 4)( ) . The use of personal computers, for example, is a(n) 5)( ) ; a fad, on the other hand, could be the use of 6)( )types of computer games.