Propose the plausible β structure of the disaccharide that contains two cyclic D-galactose sugars that are linked via the β-1,4 glycosidic bond. Explain why this disaccharide is a reducing sugar, while the sugar below is not reducing sugar.

• A. This disaccharide is a reducing sugar because it is connected via the β-1,4 glycosidic bond, while the given monosaccharides are nonreducing because there is no β-1,4 glycosidic bond.
• B. This disaccharide is a reducing sugar because, by nature, disaccharides are reducing sugars, while the given monosaccharides are nonreducing sugars.
• C. This disaccharide is a reducing sugar because it has a cyclic hemiacetal group that can be hydrolyzed into a straight-chain saccharide, while the given monosaccharides are nonreducing acetals.
• D. This disaccharide is a reducing sugar because it has a cyclic acetal group that can be hydrolyzed into a straight-chain saccharide, while the given monosaccharides are nonreducing hemiacetals.