Consider those functions f that satisfy f(x \plus{} 4) \plus{} f(x \minus{} 4) \equal{} f(x) for all real x. Any such function is periodic, and there is a least common positive period p for all of them. Find p.
<spanclass=′latex−bold′>(A)</span>8<spanclass=′latex−bold′>(B)</span>12<spanclass=′latex−bold′>(C)</span>16<spanclass=′latex−bold′>(D)</span>24<spanclass=′latex−bold′>(E)</span>32