If x^2 - 16 > 0, which of the following must be true?

a.) -4 > x > 4
b.) -4 > x < 4
c.) -4 < x < 4
d.) 4 < x

The left hand side of the equation is a difference of two squares and may be factored out as follows,
                              (x - 4)(x + 4) > 0
They may be individually taken as,
                                     x - 4 > 0    ; x > 4
                                     x + 4 > 0   ; x < -4
Thus, the answer to this item is letter A.