They form the material which forms skins, muscles, hair and nails in animals.

The correct answer is A. Protein.

Proteins are the building blocks of the body. They are made up of amino acids, which are the building blocks of life. Proteins are found in all parts of the body, including the skin, muscles, hair, and nails. They are essential for growth, repair, and maintenance of the body.

Carbohydrates are a type of nutrient that the body uses for energy. They are made up of carbon, hydrogen, and oxygen atoms. Carbohydrates are found in foods such as bread, pasta, rice, potatoes, and fruit.

Fats are a type of nutrient that the body uses for energy. They are also used to build cell membranes and to produce hormones. Fats are found in foods such as butter, oil, meat, and dairy products.

Vitamins are a type of nutrient that the body needs in small