Which of these statements is best?

Select one:

a. Slack is the time an activity can be delayed without impacting the completion time of the project.

b. In PERT, we assume that the project completion time can be modeled by the beta distribution.

c. In PERT, the variance in completion time is equal to the variance of the most time-consuming activity on the critical path.

d. The variance of the project completion time is equal to the sum of the variances of all the activities.