The Answer is D
The sound vibrations enter the ear, guided by the pina. These vibrations cause the ear drum (a thin membrane) to vibrate. The vibrating ear drum make the three ear ossicles (the hammer, anvil and stirrup bones) to vibrate in turn. These ear ossicles amplify the sound so that even very quiet sounds can be heard. The eustation tube (which leads to the back of the mouth) helps keep the pressure of the middle ear constant. The ear ossicles in turn make the round window of the cochlea vibrate. The vibrations enter the cochlea which is a coiled fluid filled tube. Vibrations travel better in a liquid than in a gas. The vibrations which travel through the cochlea, make sensitive cells which line the tube vibrate. The cells are sensitive to a particular frequency of vibration and so a number of cells may vibrate when hearing a particular sound. The cells send impulses via the auditory nerve to the brain.
tympanic membrane, also called eardrum, thin layer of tissue in the human ear that receives sound vibrations from the outer air and transmits them to the auditory ossicles, which are tiny bones in the tympanic (middle-ear) cavity
