An unstretched string fixed at both ends resonates at a fundamental frequency of 220 Hz. Which of the following will reduce the fundamental frequency?
(a) Double the tension and double the length.
(b) Halve the tension and keep the length and the mass per unit length fixxed.
(c) Keep the tension and the mass per unit length fixed and double the length.
(d) Keep the tension and the mass per unit length fixed and halve the length.