I think B is the answer. We know the left side of the equation,
sqrt((x-3)^2) = +/- (x-3) = (x-3) or (3-x),
which are the positive and negative square roots of (x-3)^2. Since the radical sign refers to the positive square root, we are asked if the positive square root is equal to 3-x. So, if we know the sign of 3-x, we can answer the question.
(1) is not sufficient, but (2) gives us that x<0 as you pointed out. Therefore 3-x must be greater than 0, so that 3-x is the positive square root of (x-3)^2.
