Suppose a differentiable function f satisfies f′(x)>0 for every x in the interval (2,5). Which of the following statements about f on (2,5) is true?
a) f is concave up on (2,5).
b) f is decreasing on (2,5).
c) f is increasing on (2,5).
d) f attains a relative maximum at every point of (2,5).