Which one of the following statements is true about the Project Evaluation and Review Technique $($PERT$)?$

a$.$

Pert uses discrete duration time estimates.

b$.$

Using the PERT weighted average for activity duration estimates removes the risk of uncertainty in activity estimates.

c$.$

PERT applies the critical path method to a weighted average duration estimate.

d$.$

The application of PERT requires the assumption of a bell curve for activity duration estimates