A researcher is curious about the effect of sleep on students' test performances. He chooses 60 students and gives each two tests: one given after two hours' sleep and one after eight hours' sleep. The test the researcher should use would be
(Choose 1 answer)
A. A related samples test.
B. A pooled-variance t test.
C. A separate-variance t test.
D. F-test for the ratio of two variances.
E. None of the other choices is correct.
