The set B={1,2,3,4,5,6,7,8,9,10,11,12} is partitioned into the four subsets {1,2,3},{4,5,6},{7,8,9},{10,11,12}. Let R be the equivalence relation that relates two elements whenever they lie in the same subset. How many ordered pairs are there in R?
a) 48
b) 36
c) 24
d) 12