The part of the ear that contains receptors that convert the fluid motion into action...

Explanation

The ear is an important organ that helps us to hear sounds. The ear is divided into three parts: the outer ear, the middle ear, and the inner ear. The part of the ear that contains receptors that convert the fluid motion into action potential is called the cochlea. The cochlea is located in the inner ear and is shaped like a snail shell. It is filled with fluid and lined with tiny hair cells that are sensitive to vibrations. When sound waves enter the ear, they cause the fluid in the cochlea to move, which in turn causes the hair cells to bend. This bending of the hair cells generates electrical signals which are sent to the brain via the auditory nerve, where they are interpreted as sound. The other options listed in the question are also important parts of the ear, but they do not contain receptors that convert fluid motion into action potential. The auditory nerve is responsible for transmitting the electrical signals generated by the hair cells to the brain. The ossicles are three small bones in the middle ear that amplify sound vibrations. The semicircular canals are responsible for our sense of balance and help us to maintain our equilibrium. The oval window is a membrane between the middle ear and the inner ear that transmits sound vibrations from the ossicles to the cochlea. Therefore, the correct answer to the question is option D: Cochlea.