A random sample of 64 students at a university showed an average age of 25 years and a sample standard deviation of 2 years. The 98% confidence interval for the true average age of all students in the university is:
a. 20.5 to 26.5
b. 24.4 to 25.6
c. 23.0 to 27.0
d. 20.0 to 30.0