## **Core Concept**
The composition of milk, including the proportion of whey protein, is an important aspect of nutrition and biochemistry. Whey protein is a key component of milk protein, known for its high nutritional value and role in various biological processes.

## **Why the Correct Answer is Right**
Cow's milk contains approximately 3.2% protein, of which about 20% is whey protein. The main proteins in milk are casein (about 80%) and whey proteins (about 20%), which include **β-lactoglobulin**, **α-lactalbumin**, and others. Therefore, if we consider the protein content of cow's milk to be around 3.2%, then 20% of this would be whey protein, which equates to roughly **0.6-0.7%** of the total milk volume.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a much higher percentage than what is typically found in cow's milk, which already makes it suspect.
- **Option B:** This is lower than the correct percentage of whey protein found in cow's milk.
- **Option D:** This option suggests a much lower percentage than the established amount.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **whey protein** is rich in essential amino acids and has a high biological value, making it a popular dietary supplement among athletes and individuals looking to increase their protein intake. Whey protein is also used in the management of certain clinical conditions due to its nutritional benefits.

## **Correct Answer:** C. 0.6%