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
Formaldehyde gas sterilization is employed for? 
Select and explain. 
A. Sterilizing hea lung machines, B. Glass materials, C. Paper and cloth, D. Fumigation of operation theater
D: Fumigation of operation theater
Answer: D: Fumigation of operation theater 
Explanation: Formaldehyde gas is used for sterilising instruments and heat sensitive catheters and for fumigating wards and sick rooms and laboratories REF:Ananthanarayan and Panicker's Textbook ofMicrobiology 8thEdition pg no:36