The correct answer is: C. Zero
The critical path is the longest path through a project network diagram. It is the path that determines the earliest possible completion date for the project. Activities on the critical path have zero total float. This means that any delay to an activity on the critical path will delay the completion of the project.
Positive total float means that an activity can be delayed without delaying the completion of the project. Negative total float means that an activity cannot be delayed without delaying the completion of the project.
I hope this helps!