Which of these statements is best?
a. Slack is the time an activity can be delayed without impacting the completion time of the project.
b. The variance of the project completion time is equal to the sum of the variances of all the activities.
c. In PERT, we assume that the project completion time can be modeled by the beta distribution.
d. In PERT, the variance in completion time is equal to the variance of the most time-consuming activity on the critical path.