David wants to estimate the mean of scores on a standardized test. He knows the population standard deviation for the test is 4. He asks his friends what they scored on the test, and gets the following answers from five friends: 15, 7, 9, 10, 5. Within which scores can David be 95% confident that the mean lies?

a. 5.7 to 12.7

b. 4.5 to 13.9

c. 4.1 to 14. 8

d. 3.5 to 16.3