Suppose we want a 90% confidence interval for the average amount of time (in minutes) spent per week on homework by the students in a large introductory statistics course at a large university. The interval is to have a margin of error of 2 minutes, and the amount spent has a Normal distribution with a standard deviation ? = 30 minutes. The number of observations required is closest to
A. 25.
B. 30.
C. 609
D. 865.