A is wrong since the slopes are clearly different, f(x) goes up by 3 every time while g(x) goes up by 1 every time.
B is also wrong since they are both going up, if they were opposites, one would be going up while the other went down.
C is also wrong since the y-intercepts are not the same, in f(x), the y-intercept is at (0,-4), and in g(x) the y-intercept is at (0,4).
That only leaves D which is the correct answer.