**Core Concept**
Lactose is a disaccharide sugar found in milk and other dairy products, composed of glucose and galactose molecules. It is an important carbohydrate source for infants and a common dietary component in many cultures.

**Why the Correct Answer is Right**
Lactose is commonly referred to as "milk sugar" because it is the primary sugar present in milk, particularly in human breast milk and cow's milk. The enzyme lactase breaks down lactose into glucose and galactose, which are then absorbed by the body. Lactose intolerance occurs when individuals lack sufficient lactase enzyme to digest lactose, leading to symptoms like bloating and diarrhea.

**Why Each Wrong Option is Incorrect**
* **Option A:** Fructose is a simple sugar found in fruits and honey, but it is not referred to as "milk sugar."
* **Option B:** Sucrose is a disaccharide composed of glucose and fructose, but it is not specifically associated with milk.
* **Option C:** Maltose is a disaccharide composed of two glucose molecules, but it is not found in milk or referred to as "milk sugar."

**Clinical Pearl / High-Yield Fact**
Lactose intolerance is a common condition worldwide, especially in individuals of African, Asian, or Native American descent, due to a genetic deficiency of lactase enzyme.

**Correct Answer: C. Maltose is not the correct answer, but the question stem asked for "milk sugar" and that is lactose. However lactose is not given as an option. Given the options, none are correct. I will provide an example of how to answer this type of question.**

**Correct Answer:** None of the above, but the correct answer is lactose.