Let's assume that a is an even prime integer and b is an odd prime integer, their subtraction results in an odd integer and an odd integer multiplied by an even integer yields an even integer.
If a and b are unique prime integers, which of the following must be even?

[A] a−b
[B] a−2b
[C] 2a−2b
[D] 2a−b
[E] ab^2