For a twice-differentiable function f, suppose f′(c)=0 and f′′(c)>0 for some real number c. Which of the following statements about the graph of f at x=c is most accurate?
a) x=c is a point of inflection of f.
b) f has a local minimum at x=c.
c) The graph of f is increasing at x=c.},{
d) f has a local maximum at x=c.