Let ga(x)=x3−3ax be defined on the closed interval [−2,2], where a is a real parameter. Which of the following lists all x-values that are guaranteed to be candidates for the absolute extrema of ga on [−2,2], regardless of the value of a?
a) {−2,a}
b) {−2,2}
c) {−2,2,0}
d) {a,−a}