Which statement best describes where the absolute extrema of a differentiable function g defined on a closed interval [c,d] can occur?
a) Only at points where g′(x)=0 inside (c,d)
b) Only at the endpoints x=c and x=d
c) At the endpoints x=c or x=d and at any points in (c,d) where g′(x)=0
d) At points where g′′(x)=0 inside (c,d)