This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'Cardiac output is increased in \nSelect and explain. \nA. Sleep, B. Pregnancy, C. Sitting, D. Standing', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Conditions that increase cardiac output exercise Anxiety Emotion and excitement Increased environmental temperature After eating Pregnancy Conditions that decrease cardiac output standing from lying posture Excessive sweating. Conditions that do not change cardiac output sleep Mild to moderate change in environmental temperature Ref: TEXTBOOK OF MEDICAL PHYSIOLOGY GK PAL VOLUME 2 PAGE 788', 'role': 'assistant'}]