A. x - (- x) is <em>the equivalent of x + x</em>, because subtracting a negative number is the same as adding it's positive counterpart. Therefore, <em>it will be 2x, not -x</em>.
B. Same thing. But this time, 0 - (- x) is the same as 0 + x, which is x, not -x.
Because <em>neither are right</em>, the only answer is C.
