Solution

disaccharide (also called a double sugar or bivose) is the sugar formed when two monosaccharides (simple sugars) are joined by $$\text{glycosidic linkage.}$$
Lactose, the disaccharide of milk, consists of galactose joined to $$\text{glucose by a β-1,4-glycosidic linkage.}$$ Lactose is hydrolyzed to these monosaccharides by lactase in human beings