The average weight of a certain number of students in a group was 72 kg . If 11 students, with an average weight of 76 kg each, leave the group , and 5 students , each with an average weight of 79 kg, join the group, the average weight of the students in the group decreases by 0.6 kg. The number of students initially in the group was:
A21
B25
C17
D19