3行2列的矩阵A，修改A的列号为"甲","乙","丙"的命令是： A: rowname(A) <-c("甲","乙","丙") B: rownames(A) <-c("甲","乙","丙") C: colname(A) <-c("甲","乙","丙") D: colnames(A) <-c("甲","乙","丙")

要把数据框x的行名修改为："甲", "乙", "丙"的语句是： （ ） A: rownames(x) <- c("甲", "乙", "丙") B: names(x) <- c("甲", "乙", "丙") C: colnames(x) <- c("甲", "乙", "丙") D: rowname(x) <- c("甲", "乙", "丙")