If f is twice differentiable and f′′(x)>0 for all x in the interval (2,5), which of the following statements about the graph of f on (2,5) is correct?
a) f has an inflection point at x=3.5 on (2,5).
b) The graph of f is concave down on (2,5).
c) The graph of f is concave up on (2,5).
d) The graph of f is increasing on (2,5).