The Following Table Shows the Enrollment in a Private College $S_{n}$

Multiple Choice

The following table shows the enrollment in a private college for the years 1996 to 2005. Interpret these figures as partial sums, $S_{n}$ , of terms of a sequence, $a_{n}$ , where $n$ is the number of years since 1995 (so $S_{1}=4194, S_{2}=4220$ , etc.) .

Which of the following gives the average enrollment between 1998 and 2001 ?

A) $\frac{S_{4}+S_{5}+S_{6}+S_{7}}{4}$
B) $\frac{S_{3}+S_{4}+S_{5}+S_{6}}{4}$
C) $\frac{a_{4}+a_{5}+a_{6}+a_{7}}{4}$
D) $\frac{a_{3}+a_{4}+a_{5}+a_{6}}{4}$