If TL is the latest allowable event occurrence time, total activity slack(s), is equal to

ANS:D - all the above.

Late start - early start.
Late finish - early finish.
Latest allowable event - early finish.

Total slck can be + or -ve.

Total slack is the amount of time the whole project can be delayed without pushing the end date of the project. This is calculated by using early and late starts and early and late finishes for tasks. Total slack is calculated as the smaller value of the late finish minus the early finish when compared to early start minus the late start.