Correct Answer: internal ear

Solution : The correct option is internal ear.

Sea sickness is primarily due to the effect of the motion of a ship on a person's inner ear, specifically the vestibular system, essential for balance and spatial orientation.The contradiction between the motion detected by the inner ear and the steady environment perceived by the eyes causes sea sickness, resulting in sensations such as nausea and dizziness. It has semicircular canals filled with fluid and sensory receptors that help the brain sense motion and balance. When being aboard a ship, the vessel's motion, such as rocking or swaying, might cause a sensory conflict in the inner ear. Although the inner ear detects motion, the eyes may perceive a pretty steady world, especially if one is indoors or in a cabin with no good view of the horizon leading to symptoms of motion sickness, such as nausea, dizziness, and vomiting.