This GRE quantitative question requires you to understand how the units digit of integers change when they are squared.

If $n$ is a positive two digit integer, then which of the following CANNOT be the units digit of $n^2$?

- $\quad 3$
- $\quad 7$
- $\quad 8$

- $\quad \textrm{I only}$
- $\quad \textrm{II only}$
- $\quad \textrm{I and II only}$
- $\quad \textrm{II and III only}$
- $\quad \textrm{I, II, and III}$