To answer this question very quickly, we must know about what is called the discriminant. The discriminant is the part of the quadratic equation that is under the square root symbol, b^2-4ac. Using the discriminant, we can find out how many solutions, or zeros, there are for a function. If the discriminant is positive, there are 2 solutions, if the discriminant is equal to 0, there is 1 solution, and if the discriminant is negative, there are no solutions. The question tells us that the equation has exactly one solution, so the discriminant must equal 0. When we write this out we get b^2 – 4ac = 0. If we add 4ac to both sides we can see that it will be the same as answer choice C, which is the correct answer.