When most monosaccharides are in a solution, they tend to form ring structures. Ribose, for example, forms a five-membered ring, which is known as Ribofuranose
The five-membered ring structure of ribose is called ribofuranose. In contrast, a six-membered ring is referred to as glucopyranose (Option A). Glyceradehyde (Option C) and acetaldehyde (Option D) are not related to the ring structures of ribose or other common monosaccharides.