2. If 9 students are to be assigned to three different factories for social practice activities, with three students at each factory, then the number of different allocation schemes is ( ).
(A) $\mathrm{C}_{9}^{3} \mathrm{C}_{6}^{3} \mathrm{C}_{3}^{3}$
(B) $3 \mathrm{C}_{9}^{3} \mathrm{C}_{6}^{3} \mathrm{C}_{3}^{3}$
(C) $\mathrm{C}_{9}^{3} \mathrm{C}_{6}^{3} \mathrm{C}_{3}^{3} \mathrm{~A}_{3}^{3}$
(D) $\frac{\mathrm{C}_{9}^{3} \mathrm{C}_{6}^{3} \mathrm{C}_{3}^{3}}{\mathrm{~A}_{3}^{3}}$
First, select three students from nine to go to the first factory, then select three students from the remaining six to go to the second factory, and the remaining three students will go to the third factory, there are $\mathrm{C}_{9}^{3} \mathrm{C}_{6}^{3} \mathrm{C}_{3}^{3}$ ways.