The brain's inexperience in interpreting messages from the weightless is the cause of the space sickness commonly experienced by two-thirds of all space travelers. A. hair cells B. otoliths C. Eustachian tube D. cochlea

Answer: B. otoliths

Correct Question: The brain's inexperience in interpreting messages from the weightless otoliths is the cause of the space sickness commonly experienced by two-thirds of all space travelers.

Explanation: The otolith is a part of the inner ear in vertebrates. This structure is responsible for directing hair cells towards the direction of gravity which in turn ensures balance. It also serves as a gauge to understand information about a person's environment. When in space, and as the gravity changes to weightlessness, the lack of a direction of gravity affects the otolith, giving a human a lack of balance and inducing motion sickness symptoms.