An unknown tuning fork sounded with a 256Hz fork produces 8 beats per second. After the unknown fork is lightly filed, the beat frequency falls to 4 beats per second. Which statement about the original frequency of the unknown fork is correct?
(a) It was higher than 256Hz.
(b) It was exactly 256Hz.
(c) It was lower than 256Hz.
(d) The information is insufficient to decide.