A study of 50 professors showed that the time they spent on the average in creating test questions was 12.0 minutes per question. the standard deviation of the population is 0 = 1.
which of the following is the 99% confidence interval for the average number of minutes it takes to create a test question?

a. (11.34,12.66)
b. (11.75,12.25)
c. (11.64,12.36)
d. (9.42,14.58)