The function h(x)=x4−4x2+1 has critical points where h′(x)=0. Which of the following correctly states the nature of these critical points?
a) Local maxima at x=±2 and a local minimum at x=0
b) Local minima at x=±2 only; x=0 is not an extremum
c) Local minima at x=±2 and a local maximum at x=0
d) Local minima at x=0 and x=±2