题目5单选题
设随机变量<img src="https://tihai-oss-cloud.itihey.com/img/b9f8e317c95ada80f5edc257a4ed55ec.png">,<img src="https://tihai-oss-cloud.itihey.com/img/6781b17cb9c3fe4ccd0013f90d1c6df5.png">,则<img src="https://tihai-oss-cloud.itihey.com/img/c4c80baaf20840fec1c5b671a6503381.png">的值为( )A. <img src="https://tihai-oss-cloud.itihey.com/img/326005cf559d5a6686d3307947807650.png">B. <img src="https://tihai-oss-cloud.itihey.com/img/db2e5d3a74d97485543871a79f96c21f.png">C. <img src="https://tihai-oss-cloud.itihey.com/img/87f108d00c4023b9573db219ca14962b.png">D. <img src="https://tihai-oss-cloud.itihey.com/img/4ceabcbea03feb572af35bc5f9c7a135.png">