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 these are true.

The answer is C) If f and g are increasing on the interval (a, b), then f + g is increasing on (a, b).
If f'(x) >0 on the interval, and f'(g) >0, then f' + g' > 0 on the interval as well. If both functions are increasing on the interval, then their sum is increasing as well.

A is wrong because the absolute max/min could be outside the interval (a,b). 
B is wrong because is f'(x) >0, then f is increasing on the interval.