单选题
设随机变量X的分布函数为
【正确答案】
A
【答案解析】[解析] 由已知得
记
，则
f X (x)=αf 1 (x)+(1-α)f 2 (x)，
故
E(X 1 )=0，D(X 1 )=1，E(X 2 )=1，D(X 2 )=4．
记
，则
f X (x)=αf 1 (x)+(1-α)f 2 (x)，
故
E(X 1 )=0，D(X 1 )=1，E(X 2 )=1，D(X 2 )=4．