There are six students, P, Q, R, S, T and U who have a different number of pens - 2, 4, 5, 7, 9 and 12 (not necessarily in the same order). The number of pens Q has is a prime number. U has 2 more pens than Q. The number of pens R has is a multiple of 4 but not a multiple of 3. P has fewer pens than Q but has more pens than S. Who has the highest number of pens?
AP
BQ
CS
DT