iF n is A positivE intEgEr, is thE vAluE oF B-A At lEAst twiCE thE vAluE oF 3n-2n (1)A=2n+1 AnD B=3n+1
(2)n=3
A.条件(1)充分,但条件(2)不充分.
B.条件(2)充分,但条件(1)不充分.
C.条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来充分.
D.条件(1)充分,条件(2)也充分.
E.条件(1)和条件(2)单独都不充分,条件(1)和条件(2)联合起来也不充分.