In an experiment to assess the effect of diet on blood pressure, 154 adults were placed on a diet rich in fruits and vegetables. A second group of 154 adults was placed on a standard diet. The blood pressures of the 308 subjects were recorded at the start of the study. I Light weeks later, the blood pressures of the subjects were measured again and the change in blood pressure was recorded for each person. Subjects on the fruits-and- vegetables diet had an average drop in systolic blood pressure of 2.8 mm Hg more than did subjects on the standard diet. A 97.5% confidence interval for the difference between the two population means is (0.9, 4.7). Interpret this confidence interval. That is, explain w hat the numbers in the interval mean.