21.3.1 * Five boys and two girls stand in a row, with boy A must stand in the middle, and the girls must be adjacent. How many different ways are there to arrange them!
A girl can stand on either the left or right side of A, and there are two possible positions regardless of which side she chooses. The two girls can also swap positions. Once they are positioned, the other 4 boys have $\mathrm{P}_{4}$ ways to stand, so in total there are $2 \times 2 \times 2 \times$ $\mathrm{P}_{4}=192$ ways to arrange them.