Answer: B
Explanation: if you look at A and try to combine like terms, you will add the -x on the right side the the one on the left, cancelling out the x on the left. then you have 0=x+0, and unless x=0, it is not true.
With B, when you add x to the -x, you cancel it out, giving you 0=0, which is true. hope it helps!
