Lactose is a sugar found in which substance?

Lactose is a disaccharide sugar composed of glucose and galactose, and it is primarily found in milk and dairy products. The presence of lactose in milk serves a nutritional purpose, providing energy and aiding in the absorption of certain nutrients, such as calcium. While other food sources do contain sugars, lactose specifically is distinctive to the milk of mammals.

Fruit typically contains fructose and glucose, while vegetables tend to have other types of carbohydrates. Grains are primarily sources of starch and do not naturally contain lactose. Therefore, milk is the correct choice when identifying the source of lactose.