Final answer:
To find the free slack or float for each activity in a network diagram, you should calculate the early start and late start times.
Step-by-step explanation:
The correct answer to find the free slack or float for each activity in a network diagram is B) Early start and late start times.
Free slack or float refers to the amount of time an activity can be delayed without delaying the project completion time. It is calculated by subtracting the early start time from the late start time for each activity.
For example, if an activity has an early start time of day 2 and a late start time of day 5, then the free slack or float for that activity would be 3 days.