Choice C is correct. It's given that a quadratic function models the height, in feet, of an object above the ground in terms of the time, in seconds, after the object is launched off an elevated surface. This quadratic function can be defined by an equation of the form , where is the height of the object seconds after it was launched, and , , and are constants such that the function reaches its maximum value, , when . Since the model indicates the object reaches its maximum height of feet above the ground seconds after being launched, reaches its maximum value, , when . Therefore, and . Substituting for and for in the function yields . Since the model indicates the object has an initial height of feet above the ground, the value of is when . Substituting for and for in the equation yields , or . Subtracting from both sides of this equation yields . Dividing both sides of this equation by yields . Therefore, the model can be represented by the equation . Substituting for in this equation yields , or . Therefore, based on the model, seconds after being launched, the height of the object above the ground is feet.
Choice A is incorrect and may result from conceptual or calculation errors.
Choice B is incorrect and may result from conceptual or calculation errors.
Choice D is incorrect and may result from conceptual or calculation errors.