Which one of the following statements is true? a. if f is continuous on (a, b), then f attains an absolute maximum value and f attains an absolute minimum inside the interval (a, b). b. if f '(x) > 0 on the interval (a, b), then f is decreasing on the interval (a, b). c. if f and g are increasing on the interval (a, b), then f + g is increasing on (a, b). d. none of the above.