已知： score <- data.frame(student = c("A", "B", "C", "D"), gender = c("M", "M", "F", "F"), math = c(90, 70, 80, 60), Eng = c(88, 78, 69, 98), p1 = c(66, 59, NA, 88))     则sort(score$math)的结果是_____。
选项：

A:90, 70, 80, 60
B:60, 70, 80, 90
C:90, 80, 70, 60
D:80, 70, 90, 60