Which of these sets of ordered pairs are functions?
R={(0, 0), (1, 1), (2, 2)}
S={(0, 1), (1, 2), (2, 3)}
T={(0, 1), (0, 2), (0, 3)}
A. only set S
B. only sets R and S
C. only sets S and T
D. sets R, S, and T