A simple PM 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. O a. The critical path is D-, duration 15 © b. The critical path is D-F, duration 12 • c. The critical path is D-E-F, duration 13.5. O d. The critical path is D-E-E, duration 15.