2. Place 10 identical balls into 3 boxes numbered $1, 2, 3$ (all 10 balls must be placed each time), with the requirement that the number of balls in each box is no less than the box's number. The number of such arrangements is
A. 9
B. 12
C. 15
D. 18
2. C First, put 1, 2, 3 balls into 3 boxes numbered $1,2,3$, respectively, and there are still 4 balls left. Consider the non-negative integer solutions of the equation $x_{1}+$ $x_{2}+x_{3}=4$, there are $C_{6}^{2}=15$ ways to distribute them.