A recent pilot study tested whether walking daily improved systolic blood pressure. For the three subjects in the study, their resting systolic blood pressure was measured at the beginning of the study and again after participating in a walking program Subject Before After for 3 weeks. The table shows the results. a. Explain why the three "before" observations and the three "after" observations are dependent samples. A. The observations are dependent samples because their values are relatively close to one another. B. The observations are dependent samples because the same subjects are used in the before and after observations. OC. The observations are dependent samples because there are three observations in each group. D. The observations are not dependent samples. b. Find the sample mean of the before scores, the sample mean of the after scores, and the sample mean of d = before - after. The sample mean of the before scores is The sample mean of the after scores is The sample mean of d is . (Round to the nearest integer as needed.) 1 145 110 2 170 150 3 135 145