Which of the following scenarios describes a condition in which resonance can occur? a. two tuning forks are struck simultaneously, one with a frequency of 659hz and one with a frequency of 639hz, causing beats. b. an isolated tuning fork is struck with a mallet, causing it to vibrate strongly at 659hz. c. two tuning forks that vibrate at the same frequency are near to each other. one tuning fork is struck with a mallet so that it vibrates. d. a tuning fork is over a column of air that is 9/2 the wavelength of the wave produced by the tuning fork.