Answer:
The fourth graph (see the attached figure)
Explanation:
we know that
In the quadratic equation of the form
The discriminant D is equal to

If D=0 -----> the quadratic equation has only one real solution
If D> 0 ---> the quadratic equation has two real solutions
If D< 0 ---> the quadratic equation has two complex solutions
therefore
The first graph has two real solutions (x=-2 and x=3) then the discriminant is greater than zero
The second graph has two real solutions (x=-2 and x=2), then the discriminant is greater than zero
The third graph has no real solutions, then the discriminant is less than zero
The fourth graph has only one real solution (x=1), then the discriminant must be equal to zero