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: Microbiology
[{'content': 'By using phase contrast microscope: \nSelect and explain. \nA. Internal structures are differentiated in living cells, B. Internal structures are differentiated in dead cells, C. Internal metabolic activities can be observed, D. External capsule formation can be observed', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]