问题:
[单选题]
代码 x <- matrix(1:20,ncol=4);apply(x,2,mean)的运行结果是
A3 8 13 18
B8.5 9.5 10.5 11.5 12.5
C16 17 18 19 20
D1 2 3 4 5
代码 x <- matrix(1:20,ncol=4);apply(x,2,mean)的运行结果是
A3 8 13 18
B8.5 9.5 10.5 11.5 12.5
C16 17 18 19 20
D1 2 3 4 5
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