Consider the function f(x)=x4+2x2+5. Which statement about its local extrema is correct?
a) f has two local minima at x=−1 and x=1 and a local maximum at x=0.
b) f has no critical points and hence no local extrema.
c) f has exactly one local minimum at x=0 and no local maximum.
d) f has exactly one local maximum at x=0.