Identify the following statement that is true or false for an arbitrary function f with a, b, and c as arbitrary constants. Explain your answer or provide a counterexample.
a. All functions of the form f(x) = ax² + bx + c are quadratic.
b. If a = 0, then the function f(x) = ax² + bx + c is linear.
c. If b = 0, then the function f(x) = ax² + bx + c is quadratic.
d. If c = 0, then the function f(x) = ax² + bx + c is cubic.