Answer:
Option D
Explanation:
SO we have to solve to know;
a. The formula is;

Slope =
=
= -3
So A is not the answer!
b. The formula is;

Slope =
=
So B is not the answer!
c. The formula is;

Slope =
=
=

So C is not the answer!
d. The formula is;

Slope =
=
= 0
So D is the correct answer!!!