A guitar string of length L, with both of its ends fixed, is vibrating, producing a sound composed of a fundamental frequency and its integer multiples (harmonics). To emphasize all the even-numbered harmonics at the expense of the odd-numbered ones, the furthest distance away from either end where one should hold down the string is
(a) L/2.
(b) L/3.
(c) L/4.
(d) L/5.