23. A frog jumps on a $3 \times 3$ grid, each time randomly choosing one of the four directions: up, down, left, or right, but it cannot jump diagonally. If the frog chooses a direction that would take it off the grid, it "wraps around" to the opposite side. For example, if the frog starts from the center and jumps "up" twice, it first jumps to the middle of the first row, and then to the middle of the third row. Suppose the frog starts from the center and makes at most four random jumps, and stops when it lands on one of the corner positions. What is the probability that the frog lands on a corner position at least once in four jumps?
(A) $\frac{9}{16}$
(B) $\frac{5}{8}$
(C) $\frac{3}{4}$
(D) $\frac{25}{32}$
(E) $\frac{13}{16}$
23. D.

In a $3 \times 3$ grid, label the center cell, the middle cells, and the corner cells as $M$, $E$, and $C$ respectively, as shown in Figure 7. Then, the scenarios where the frog jumps to a corner cell once in four jumps are $E C$, $E E C$, $E E E C$, and $E M E C$.
Thus, the required probability is
$$
\begin{array}{l}
1 \times \frac{1}{2}+1 \times \frac{1}{4} \times \frac{1}{2}+1 \times \frac{1}{4} \times \\
\frac{1}{4} \times \frac{1}{2}+1 \times \frac{1}{4} \times 1 \times \frac{1}{2} \\
=\frac{25}{32}
\end{array}
$$