Mark is conducting an experiment on how a new medicine can treat patients suffering from the flu. He has 3 groups of patients who are infected with the same flu strain, with 7 patients in each group. He gives the medicine to all of the patients in one group. The treated patients experienced an improvement in their symptoms, and the patients in the untreated groups have not. Is there a sampling bias in the situation above? A. No, all 3 groups have the same number of patients who all suffer from the same flu strain. B. Yes, the medicine may not work on the patients in the other two groups. C. Yes, the patients in the other 2 groups have different strains of the flue than the treated patients. D. There is not enough information to determine if the sample is biased.