If c and d are unique prime integers, which of the following must be even?
Options:
(A) c−d
(B) 2c−2d
(C) c−2d
(D) 2c−d
(E) cd^2 OK. Let's think. Some random thoughts first:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Any number multiplied by 2 has to be an even number The answer: (B).