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
Electron microscopy was introduced by: 
Select and explain. 
A. Leeuwenhoek, B. Robert Koch, C. Ruska, D. Paul Ehrlich
C: Ruska
Answer: C: Ruska 
Explanation: 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. 
The apparatus was the first practical demonstration of the principles of electron microscopy.