If n is a positive integer, which of the following expressions must be even?  Select the correct option:
A) (n − 3)( n + 1)
B) (n − 8)( n + 1)
C) (n − 4)( n + 4)
D) (n − 5)( n + 1)
E) (n − 5)( n + 5)
Whether n is even or odd, (n-8)(n+1) will have one odd factor and one even factor.   The product will be even.   The answer is (n − 8)( n + 1).
<result>B</result>
If n is a positive integer, which of the following expressions must be even?