AMC 8 2008 Problem 19

Eight points are spaced around at intervals of one unit around a $2 \times 2$ square, as shown. Two of the $8$ points are chosen at random. What is the probability that the two points are one unit apart?

$\textbf{(A)}\ \frac{1}{4} \textbf{(B)}\ \frac{2}{7} \textbf{(C)}\ \frac{4}{11} \textbf{(D)}\ \frac{1}{2} \textbf{(E)}\ \frac{4}{7}$