Can someone help me with the answers to these true and false questions?

Determine whether each statement is true or false. You have one submission for each statement. (a) If f'(c) = 0, then f has a relative maximum or minimum at x = c. OTrue OFalse (b) If f'(x) changes from positive to negative at x = a, then f has a relative maximum at x = a. OTrue OFalse (c) If f'(x) 2 0 on (a,b), then f is increasing on the interval (a,b). OTrue OFalse (d) If f'(c) does not exist, then f(x ) has a critical point at x = c. OTrue OFalse