Explanation:
the slope is the ratio of "y coordinate difference / x coordinate difference".
so, let's find 2 good points (I mean by that with integer coordinates). I see e.g.
(-1, -1) and (0, -7)
x changes by +1 (from -1 to 0).
y changes by -6 (from -1 to -7).
so, the slope is -6/1 = -6.
D is the right answer.