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 of the second-grade students occupy the first row?
A) 25P20
B) 5P5*20P15
C) 5C5*25C14
D) 5P5*15P15
E) 5P5*25PC15