11. A, B, and their four classmates are arranged in two rows of three people each as shown in Figure 3.
If the seating arrangement is random, then the probability that A and B are adjacent in the same row or in the same column is
(A) $\frac{1}{3}$
(B) $\frac{2}{5}$
(C) $\frac{7}{15}$
(D) $\frac{1}{2}$
(E) $\frac{2}{3}$
11. C.

Only consider the positions of A and B, there are $\mathrm{C}_{6}^{2}=15$ ways in total. They are adjacent in the same row in $2 \times 2=4$ ways, and adjacent in the same column in 3 ways. Therefore, the probability that the two are adjacent is $\frac{4+3}{15}=\frac{7}{15}$.