This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Embryology, Subject name: Anatomy
[{'content': 'First organ to attain functional maturity is: \nSelect and explain. \nA. CVS, B. CNS, C. GIT, D. Lungs', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. A CVSRef: Netter's Clinical Anatomy, 3rd ed. pg. 35* CVS is the first fully functional organ system in fetus and first to attain maturity from functional perspective.", 'role': 'assistant'}]