A simple project network has three activities, A, B, and C. A is an immediate predecessor of B and of C. Bis an immediate predecessor of C. The activity durations are A-4, B-3, 6-8. O A. The critical path is A-B-C, duration 15. B. The critical path is A-C, duration 12. O C. The critical path cannot be determined without knowing PERT expected activity times. D. The critical path is A-B-C, duration 13.5 E. The network has no critical path