This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'Which immunoglobulin crosses placenta? \nSelect and explain. \nA. IgG, B. IgM, C. IgA, D. IgD', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a (IgG). (Ref. Textbook of Microbiology by Anantanarayan, 6th/82)FeaturesIgGIgAIgMIgDIgE1Sr. Cone, (mg/ml)1221.20.030.000042Half Life (Days)23652-81-53Daily Production (Meg/ Kg)34243.30.40.000234Carbohydrate (%)381213125Complement fixation - Classical++-+++--6Complement fixation - Alternative-+---7Placental Transfer+----8Heat Stability (56deg c)++++-9Synthesized earliest (phylogenetically oldest)--+--10J-chain-++- 11Secreted by seromucinous glands-+---', 'role': 'assistant'}]