Which of the following statements regarding CPM is true?

Select one:

a$.$ All activities on the critical path have their LS equal to the maximum EF of all immediate predecessors.

b$.$ Some networks have no critical path.

c$.$ The critical path is that set of activities that has positive slack.

d$.$ All activities on the critical path have their ES equal to their LF$.$

e$.$ The critical path is the shortest of all paths through the network.