Write the correct answer from the given four options:
The blood groups of 25 students are recorded as under:
A, B, O, A, AB, O, A, O, B, A, O, B, A, AB, AB, A, A, B, B, O, B, AB, O, A, B.
What is the number of students in blood group 'O'?
1
8
2
7
3
6
4
More than one of the above
5
None of the above