17 Five boys and two girls stand in a row, with boy A must stand in the middle, and the girls must be adjacent, then the number of different ways to arrange them is
A. $C_{5}^{1} P_{4}^{4} P_{2}^{2}$
B. $C_{4}^{1} P_{4}^{4} P_{2}^{2}$
C. $P_{6}^{6}$
D. $P_{5}^{5}$
17 B. The girls may stand to the left of A, or to the right of A. In either case, there are two scenarios (if on the left, they can occupy the first and second or the second and third positions from the left), and the two girls can switch places, so there are a total of $2 \times 2 \times 2 = C_{4}^{1} P_{2}^{2}$ cases.
After the girls are positioned, the 4 boys have $P_{4}^{4}$ ways to arrange themselves. The total number of arrangements is $C_{4}^{1} P_{4}^{4} P_{2}^{2}$.