In the human ear, how do different hair cells respond to different frequencies of sound?a. Waves of pressure move through the fluid in the cochlea.b. Hair cells are 'sandwiched' between membranes.c. Receptor proteins in the stereocilia of each hair cell are different; each protein responds to a certain range of frequencies.d. Because the basilar membrane varies in stiffness, it vibrates in certain places in response to certain frequencies.