38. Forty patients with high blood pressure volunteer for a study. The participants are given an injection of a placebo (a saline solution with no pharmacological effect), and an hour later their drop in blood pressure is measured. Two days later the same 40 patients are given an injection of an experimental new drug, and an hour later the drop in blood pressure is recorded. Researchers want to investigate the effect of the drug on blood pressure. They wish to compare the drop in blood pressure after the injection of the drug to the drop in blood pressure after injection of the placebo. Which one of the following is the most appropriate test? (Assume normality where necessary ). (a) A x' test with 1 degree of freedom. (b) A Z test. (c) A t test with 79 degrees of freedom. (d) A t test with 78 degrees of freedom. x (e) A t test with 39 degrees of freedom