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': 'Electron microscopy was introduced by: \nSelect and explain. \nA. Leeuwenhoek, B. Robert Koch, C. Ruska, D. Paul Ehrlich', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The first prototype electron microscope, capable of four-hundred-power magnification, was developed in 1931 by the physicist Ernst Ruska and the electrical engineer Max Knoll.\xa0\nThe apparatus was the first practical demonstration of the principles of electron microscopy.', 'role': 'assistant'}]