Simon would like to estimate the mean number of residents in apartment buildings in his city. He randomly selects four apartment buildings and finds that they have the following number of residents: 80, 65, 95, 70. Within which two numbers of residents can Simon be 99% sure that the population mean lies?

a. 38.9 to 116.1

b. 56.4 to 98.6

c. 60.3 to 94.7

d. 64.6 to 90.4