Eight points are spaced 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 points are one unit apart?
Answer Choices
A. \dfrac{1}{4}
B. \dfrac{2}{7}
C. \dfrac{4}{11}
D. \dfrac{1}{2}
E. \dfrac{4}{7}