Among the given nutrients, milk is a poor source of Vitamin C.

Option 1: Calcium - This option is incorrect. Milk is a rich source of calcium, which is important for the health and development of bones and teeth. It is often recommended as a primary source of calcium in the diet.

Option 2: Protein - This option is incorrect. Milk is also a good source of protein. It contains two types of proteins - casein and whey protein. Protein is essential for muscle growth and repair, and milk is often considered a complete protein source.

Option 3: Carbohydrate - This option is incorrect. Milk contains lactose, which is a type of carbohydrate. Lactose provides energy and is the main carbohydrate found in milk.

Option 4: Vitamin C - This option is correct. Milk is not a significant source of Vitamin C. While it does contain small amounts of vitamins and minerals, including Vitamin A and D, it is not a rich source of Vitamin C. Other food sources, such as citrus fruits and vegetables, are better sources of Vitamin C.