please solve it in 5 mins fastttttttt I will thumb you up

Copy of "A simple CPM network has four activities, A, B, C and D. A is an immediate predecessor of B and of C. B is an immediate predecessor of C and C is immiciate predecessors for D. The activity durations are A=4,B=3,C=8,D=6 ". "The critical path is A-B-G-D, duration 21." "The critical path is A-C_D, duration 18." The network has no critical path. The critical path cannot be determined without knowing PERT expected activity times. "The critical path is A-B-C, duration 13.5