Definition: In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".
Input: [header] How to choose a protein supplement [title] Choose whey protein to build muscle. [step] If you're looking for muscle-building protein, whey protein is generally your best option. Whey protein can come in the form of powder or pills and is commonly used when people are trying to build muscle via things like weight training programs. <sep> (A) By doing this, you're gaining more body fat and growing more muscle at the same time. [substeps] Whey protein can be found in half of the packaged foods. (B) Whey protein is also a low-fat protein, rich in red blood cells from bacteria. Although whey protein does not impart healthy fats to the body, whey protein helps build muscle, which you can grow and burn through exercise. (C) [substeps] Look for a whey protein powder or supplement with a high biological value. This measures how well your body can absorb the protein. (D) Whey protein occurs as a food chain, hence the slogan, " protein is fat free ". [substeps] Whey protein is complex and varies from patient to patient.
Output:
C