The correct answer is B) inner ear. Seasickness is caused by the rolling or rocking motions affecting the fluid in the inner ear, which is responsible for our sense of balance and spatial orientation. The fluid disturbance in the inner ear sends conflicting signals to the brain, leading to the symptoms of seasickness, such as nausea, dizziness, and disorientation. The other options are incorrect because the stomach, bladder, and lower intestines are not directly responsible for the primary cause of seasickness. While these body parts may be affected by seasickness, the root cause is the disturbance in the inner ear's fluid dynamics.