How can you tell when a quadratic equation has two identical, rational solutions?
when the radicand is negative
when b in the quadratic formula is greater than the radicand
when the radicand equals zero
when the radicand is not a perfect square

The discriminant of a quadratic equation determines the nature of the roots of the equation whether they are rel or imaginary. The formula for determining the discriminant is 
d = b2 - 4acwhen there are two identical real roots, then the discriminant is equal to zero. The answer is C.