A study was conducted to determine the effectiveness of a certain treatment. A group of 112 patients were randomly divided into an experimental group and a control group. The table shows the result for their net improvement. Let the experimental group be group 1 and the control group be group 2. XI Experimental Control 51 61 11.2 3.4 S 6.4 6.6 (a) Test whether the experimental group experienced a larger mean improvement than the control group at the a = 0.05 level of significance. Should the null hypothesis be rejected? OA. Yes, because the test statistic is in the critical region. B. Yes, because the test statistic is not in the critical region. OC. No, because the test statistic is not in the critical region. OD. No, because the test statistic is in the critical region. (b) Construct a 95% confidence interval about , - and interpret the results. Therefore, the confidence interval is the range from to (Round to two decimal places as needed.) What is the interpretation of this confidence interval? OA. There is a 95% probability that the difference of the means is in the interval. OB. There is a 95% probability that the difference between randomly selected individuals will be in the interval. OC. We are 95% confident that the difference between randomly selected individuals will be in the interval. OD. We are 95% confident that the difference of the means is in the interval. ?