A group of statistics students decided to conduct a survey at their university to estimate the average (mean) amount of time students spent studying per week. They sampled 554 students and found a mean of 22.3 hours per week. Assuming a population standard deviation of 6 hours, what is the 95% level of confidence?
A. [21.80, 22.80]
B. [16.3, 28.3]
C. [21.64, 22.96]
D. [20.22, 22.0]