12 What does the expression f(x) dx calculate? 12- 2 2 O A. The average value of f(x) over the interval [2,12]. O B. The instantaneous rate of change of f(x) at x = 7. O) c. The average rate of change of f(x) from x = 2 to x = 12. O D. The area under the function f(x) between x = 2 and x = 12. O E. None of the above