3. In the xy-plane, the graph of the polynomial
function f crosses the x-axis at exactly two points, (a,0) and (b,0), where a and b are both positive. Which of the following could define f?
(A)f(x)=(x-a)(x-b)
(B) f(x)=(x+ a)(x+b)
(c) f(x)=(x-a)(x+b)
D) f(x)= x(x-a)(x−b)