2021 Fermat Problem 16

If n is a positive integer, the notation n! (read "n factorial") is used to represent the product of the integers from 1 to n. That is, n! = n(n-1)(n-2)\cdots(3)(2)(1). For example, 4! = 4(3)(2)(1) = 24 and 1! = 1. If a and b are positive integers with b > a, the ones (units) digit of b! - a! cannot be

\textbf{(A)}\ 1\quad \textbf{(B)}\ 3\quad \textbf{(C)}\ 5\quad \textbf{(D)}\ 7\quad \textbf{(E)}\ 9

If there are no answer choices shown, enter a numerical answer.

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