This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
Silver impregnation technique is used in the identification of ? 
Select and explain. 
A. Spirochaetes, B. Leptospira, C. Borrelia, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Silver impregnation: cells and structure too thin to be seen under the ordinary microscope may be rendered visible if they are thickened by impregnation of silver on the surface. Such a method is used for the demonstration of spirochetes and bacterial flagella REF:Ananthanarayan & Panicker's Textbook of Microbiology 9th edition pg no:13