What is an accurate difference between the Program Evaluation and Review Technique $($PERT$)$ and critical path method $($CPM$)?$

a$.$

CPM involves more work than PERT because it requires several duration estimates.

b$.$

PERT uses different duration estimates whereas CPM uses one specific duration estimate.

c$.$

CPM addresses the risk associated with duration estimates whereas PERT does not.

d$.$

Unlike CPM$,$ PERT estimates only when there is no risk of uncertainty.