3. Fill the 9 blanks in the figure shown with the numbers $1,2, \cdots, 9$, requiring that each row from left to right and each column from top to bottom increase sequentially. When 5 is fixed in the central position of the figure, the number of ways to fill the blanks is
A. 12
B. 15
C. 16
D. 18
As shown in the figure above, 1 and 9 can only be located in the top-left and bottom-right corners, and 2 and 8 can also be placed adjacent to 1 and 9, resulting in 4 cases in total. In these cases, the places marked with $\times$ cannot place the number 3, so 3 can only be placed in the empty cells.
Considering the position of 4, the filling methods for (1) and (3) are 4 each; for (2) and (4), the filling methods are 5 each, thus the total number of ways to fill the empty cells is 18. Therefore, the answer is $D$.