A Student Took the Letters M, A, T and Wrote

Multiple Choice

A student took the letters M, A, T and wrote down the possibilities MAT, MTA, TAM, TMA, ATM, AMT from the given three letters. When the student wrote out the 6 possibilities, he was finding the

A) empirical probability.
B) historical probability.
C) combinations of M, A, T.
D) permutations of M, A, T.