118 Let $f$ be a mapping from the set $A=\{1,2,3\}$ to $A$. Denote by $F$ the set of all $f$ that satisfy the condition: "For any two elements $x_{1}<x_{2}$ in $A$, we have $f\left(x_{1}\right) \leqslant f\left(x_{2}\right)$". Then the number of elements in $F$ is
A. 8
B. 9
C. 10
D. 11
118 C. Use $(1,2,3) \rightarrow (x, y, z)$ to represent elements of $F$, where $1 \leqslant x \leqslant y \leqslant z \leqslant 3$. Therefore, $(x, y, z)$ can be $(1,1,1),(1,1,2),(1,1,3),(1,2,2),(1,2,3)$, $(1,3,3),(2,2,2),(2,2,3),(2,3,3),(3,3,3)$.