Let f be differentiable on (−4,6) with f′(x)>0 for −4<x<2, f′(2)=0, and f′(x)<0 for 2<x<6. Which of the following statements about f at x=2 is true?
a) f has an inflection point at x=2
b) No conclusion can be drawn about relative extrema at x=2
c) f has a local maximum at x=2
d) f has a local minimum at x=2