A 2010 Dutch study implies that exercising before eating protein might help the body convert more of the protein into muscle. In the study, 48 men were randomly assigned to either exercise or rest for 30 minutes. At the end of the 30 minutes, all drank a protein shake and had their muscle-protein synthesis measured. Regardless of age, exerciser's bodies converted more of the protein to muscle than the resting bodies.

(a) What are the cases in this study?

(b) What are the two main variables in this study? Identify each as categorical or quanti- tative.

(c) Which variable is the explanatory variable? Which is the response?