Answer:
C
Step-by-step explanation:
Remember that we can use the discriminant to determine the amount of roots that a quadratic function has.
If the determinant equals 0, then we only have one real root.
Our function is given by:
Then the discriminant will be:
We only have one real root, thus our discriminant must be 0:
Solve for b:
Thus:
The answer is both II and III.
The final answer, then, is C.