A pharmaceutical company wishes to study the efficacy of three types of medications (A, B, and C). It runs an experiment in which 5 subjects are are treated with medication A, another set of 5 subjects are treated with medication B, and a third set of 5 subjects are treated with medication C. The times to recover are recorded and shown below. What is the factor in this case: a b c, subjects being treated, times to recover, or medication