2.5 已知离散型随机变量X的分布律为 X=k =(p)^k+1(k=0,1), 则 p= ()-|||-(A) dfrac (sqrt {5)-1}(2) (B) dfrac (sqrt {5)+1}(4) (C) dfrac (1-sqrt {5)}(2) (D) dfrac (-1-sqrt {5)}(2)