The correct answer is: A. Its latest finish time and earliest start time for its successor activity.
Total float is the amount of time that an activity can be delayed without delaying the project’s finish date. It is calculated as the difference between the latest finish time (LFT) and the earliest start time (EST) for the activity.
The LFT is the latest time that an activity can finish without delaying the project’s finish date. It is calculated as the earliest finish time (EFT) of the successor activity plus the total float of the successor activity.
The EST is the earliest time that an activity can start without delaying the project’s finish date. It is calculated as the EFT of the predecessor activity minus the total float of the predecessor activity.
Therefore, the total float for any activity is defined as the difference between its latest finish time and earliest start time for its successor activity.
Option B is incorrect because the latest start time is not used to calculate total float.
Option C is incorrect because the earliest start time is not used to calculate total float.
Option D is incorrect because the earliest finish time is not used to calculate total float.