Which substances are necessary for the metabolism of fat, protein, and carbohydrates?

The correct choice is Pantothenic Acid (B5). This vitamin plays a crucial role in the metabolism of fats, proteins, and carbohydrates. It is a key component of coenzyme A (CoA), which is essential for the entry of fatty acids into the Krebs cycle for energy production. Additionally, pantothenic acid is involved in the synthesis of cholesterol and certain hormones, as well as the formation of acetyl-CoA, which is critical for carbohydrate metabolism and energy production.

In contrast, while Vitamin C and Vitamin B12 have important functions in the body, they are not directly involved in the metabolic processes of fats, proteins, and carbohydrates. Vitamin C is primarily known for its role as an antioxidant and in collagen synthesis, while Vitamin B12 is critical for red blood cell formation and neurological function but does not directly participate in macronutrient metabolism. Niacin, on the other hand, does contribute to metabolism through its role in energy transfer reactions (as part of NAD and NADP), but the question is best addressed with pantothenic acid due to its central role in various metabolic pathways for all three macronutrients.