Step 1: Picture what a capsule shell must do.
A capsule shell has one job, hold the medicine safely and then break down fast once it reaches the stomach so the drug can start working. This means the shell material must dissolve easily in the body.
Step 2: Think about which materials dissolve easily.
Starch is a carbohydrate that breaks down quickly in water and in the digestive tract. That is exactly why manufacturers use starch to shape capsule shells, it melts away fast once swallowed.
Step 3: Compare with the other choices.
Protein is a nutrient our body uses for growth, not a shell forming material. Egg peel is not part of any standard capsule making process. Cellulose is a fiber that resists breaking down, our body cannot digest it easily, so it works poorly as a fast dissolving shell.
Step 4: Settle on the answer.
Because starch dissolves fast and is safe to eat, it is the substance used for the capsule cover.
The correct answer is Starch.