A student monitoring group conducts a survey of a sample of 100 undergraduate students and finds that the mean amount of internet use each week was 35.1 hours with a standard deviation of 8.2 hours. Give a 99% confidence interval for the true mean time per week.

a Between 31.10 hours and 39.10 hours

b Between 32.99 hours and 37.21 hours

c Between 33.75 hours and 36.45 hours

d Between 33.49 hours and 36.71 hours