2008 AMC 8 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}\qquad\textbf{(B)}\ \frac{2}{7}\qquad\textbf{(C)}\ \frac{4}{11}\qquad\textbf{(D)}\ \frac{1}{2}\qquad\textbf{(E)}\ \frac{4}{7}

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.