Assume we want 90% confidence interval for average amount of time (in minutes) spent per week on homework by students in large introductory statistics course at the large university. The interval is to have a margin of error of 3 minutes, and the amount spent has a Normal distribution with a standard deviation ? = 40 minutes. The number of observations required is closest to
A. 22.
B. 482.
C. 683.
D. 1180.