The correct option is A A
In the given sentence the narrator mentions finishing the paper before time and being allowed to leave the hall with the supervisor's permission. Since it is an examination, it has a fixed time before which one must finish their paper. In this case, the narrator finished answering the paper before time and so the correct word to use in part [A] instead of 'before' is 'early'. Therefore, the incorrect part of the sentence is part [A] and the correct option is (A).