Which of the following statements is true? a To calculate the early start date of an activity, you add 1 to the early finish date of the previous activity. b If an activity on a network diagram has two predecessor activities, the early start date of any successor activity is the smallest early finish date of the predecessor activities. c To calculate the critical path in a network diagram, you have to compare the early start date of an activity to its early finish date. d If a project schedule changes, the network diagram's critical path will also change