A simple CPM network has three activities, D, E, and F. D is an immediate predecessor of E and of F. E is an immediate predecessor of F. The activity durations are D=4,E=3,F=8. The critical path is D-E-F, duration 15. The critical path is DF, duration 12 . Slack at D is 3 periods. Slack at E is 3 periods. Both The critical path is DEF, duration 15 and Slack at D is 3 periods are true