Exam IIA-CIA-Part2 topic 4 question 96 discussion

Which of the following statements is correct regarding the use of a program evaluation and review technique (PERT) model?
It makes use of a probability model to arrive at a realistic estimate of time necessary for completion of the audit engagement.
It requires that activities are performed in sequence such that each task is completed before the commencement of the next activity.
It remains fixed once completed to act as a baseline for measuring the performance of the audit staff following completion of the engagement.
It begins with the auditor-in-charge identifying the overall scope and then breaking down the audit engagement into identifiable activity units.