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': 'Which amongst the following is the gold standard for demonstrating hCG \nSelect and explain. \nA. Radio immuno assay, B. Latex agglutination, C. Immunoflorescence, D. ELISA', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]