The correct answer is letter D. He has trouble with his balance. This is part of the inner ear that is contains a semi-like fluid inside that is sensitive to movements and motions of the body. Inside these semi-circular canals are hair-like structures that sway or move with the fluids when it detects motion. If there is an imbalance within the membrane, a person may have problems with his balance. A condition that is also known as vertigo.