[题目] 设随机变量X服从参数为2的泊松分布,-|||-则下列结论中正确的是 ()-|||-A. (X)=0.5, D(X)=0.5-|||-B. (X)=0.5, D(X)=0.25-|||-C. E(X)=2,D(X)=4-|||-D. E(X)=2,D(X)=2