Which of the following are suitable null hypotheses. if not, explain why. a. comparing two groupsconsider comparing the average blood pressure of a group of subjects, both before and after they are placed on a low salt diet. in this case, the null hypothesis is that a low salt diet does reduce blood pressure, i. e., that the average blood pressure of the subjects is the same before and after the change in diet. b. classification. assume there are two classes, labeled + and -, where we are most interested in the positive class, e. g., the presence of a disease. h0 is the statement that the class of an object is negative, i. e., that the patient does not have the disease. c. association analysisfor frequent patterns, the null hypothesis is that the items are independent and thus, any pattern that we detect is spurious. d. clusteringthe null hypothesis is that there is cluster structure in the data beyond what might occur at random. e. anomaly detectionour assumption, h0, is that an object is not anomalous.