设P(B)>0,A1,A2互不相容,则下列各式中不一定正确的是()
( A ) P ( A1A 2/B ) = 0 ;
( B ) P ( AUA 2 B ) = P (a/B ) + P ( A 2 B ) :
( C ) P ( AA 2 B ) = 1 :
( D ) P ( A , UA 2 B ) = 1 .