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
Wards in an hospital are sterilized by the following method: 
Select and explain. 
A. Ethylene oxide gas, B. Formaldehyde fumigation, C. Washing with soap water, D. Carbolic acid spraying
B: Formaldehyde fumigation
Answer: B: Formaldehyde fumigation 
Explanation: Formaldehyde gas is used for sterilizing instruments and heat sensitive catheters and for fumigating wards, sick rooms and laboratories. Under properly controlled conditions, clothing, bedding, furniture, and books can be satisfactorily disinfected. In aqueous solutions, it is markedly bactericidal and sporicidal and also lethal effect on viruses. Ref: Textbook of Microbiology By Ananthanarayan, 6th edition, Page 29.