The correct option is A ¯¯¯¯A
The complement of occurrence an event is the non-occurrence of that event.
Formally, the occurrence of all the outcomes that are NOT favorable to the event comes under the complement of that event.
The complement of an event A is represented by ¯¯¯¯A, where the bar above A signifies the occurrence of all the outcomes that are NOT favorable to the event A.
As an example, If P(E)=rolling an even number, then P(¯¯¯¯E)=not rolling an even number
=rolling an odd number
Therefore, option (a.) is the correct choice.