A school bus has 25 seats, with 5 rows of 5 seats. 15 students from the first grade and 5 students from the second grade travel in the bus. How many ways can the students be seated if all the first-grade students occupy the first 3 rows?
A. 25P20
B. 5P5 × 20P15
C. 15C15 × 10C5
D. 15P15 × 10P5
E. 15P15 × 10C5