This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'A pilot in Sukhoi aircraft is experiencing negative G. Which of the following physiological events will manifest in such situation? \nSelect and explain. \nA. The hydrostatic pressure in veins of lower limb increases, B. The cardiac output decreases, C. Black out occurs, D. The cerebral arterial pressure rises', 'role': 'user'}, {'content': 'Answer: D \nExplanation: In negative gravity, the blood will no longer be held onto lower limbs. So lower limb venous pressure decrease and the venous return increases. This will cause the cardiac output to increase. Since no gravity, blood rushes to the head, and cause increased cerebral arterial pressure and red outs (mental confusion).', 'role': 'assistant'}]