If each digit in the set A = {1, 2, 3, 4, 5} is used exactly once, in how many ways can the 5 digits be arranged?
A. 6
B. 24
C. 72
D. 96
E. 120

(E) There are 5! = 120 possible arrangements of the five digits with no restrictions. Every time an item is selected, it is reduced from the pool. (5)(4)(3)(2)(1) = 120
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Remember the rule of combination.

In this question we deal with permutations.

A combination would be some subset of a given set (order does NOT matter). For example, selecting three numbers out of five.