Slack time is equal to:

A) the difference between an activity's latest and earliest expected completion time.
B) the latest expected completion time.
C) the difference between the start time and realistic time for each activity.
D) the sum of an activity's latest and earliest expected completion time.
E) the difference between the optimistic time and pessimistic time for an activity.

A
Explanation: A) Slack time is always calculated based upon expected completion times, using the difference to calculate the slack time.