Questions on a statistics exam are considered good questions provided the questions discriminate between students who have studied for the exam and those who have not studied. Suppose that on a particular statistics exam the students were separated into two groups, the group that studied and the other group that had not studied. Data was collected and a 95% confidence interval for the difference in the proportion of those passing the exam from the group that studied and the proportion of those passing the exam from the group that had not studied. The confidence interval turned out to be (