题目设X与Y不相关,D(X)=2,D(Y)=1,则D(X-Y+5)=【】A. 3B. 6C. 8D. 1设$X$与$Y$不相关,$D(X)=2$,$D(Y)=1$,则$D(X-Y+5)=$【】A. 3B. 6C. 8D. 1题目解答答案A. 3