To answer this question, the user needs to know about the components of milk protein.

The correct answer is:

B. Casein

Explanation:

Milk protein is made up of two main types of protein: casein and whey protein. Casein is the most abundant protein in milk, making up about 80% of the protein content. It is a slow-digesting protein that is often used in protein supplements. Milkein, Malkein, and Kazien are not correct names for milk protein.