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
Answer Choices
A. 1
B. 3
C. 5
D. 7
E. 9