Based on the confi dence intervals, we can state at a 95% level of confi dence that the mean diff erence in the population between these two groups is

a. between 0.702 and 3.144 more correct responses among those who received a reward for correct responses compared to those who did not receive a reward.

b. between 0.702 and 3.144 more correct responses among those who did not receive a reward for correct responses compared to those who did receive a reward.

c. between 0.702 and 3.144 correct responses for both groups on the test.