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: Biochemistry
6 membered ring structure of monosaccharides are known as: 
Select and explain. 
A. Pyran, B. Furan, C. Aldose, D. Ketose
A: Pyran
Answer: A: Pyran 
Explanation: The ring structures of monosaccharides are similar to the ring structures of either pyran (a six-membered ring) or furan (a five-membered ring). For glucose in solution, more than 99% is in the pyranose form. Ref: Harper 28th edition, chapter 14.