The PRIMARY reason an IS auditor performs a functional walkthrough during the preliminary phase of an audit
assignment is to:

A.
understand the business process.

B.
comply with auditing standards.

C.
identify control weakness.

D.
plan substantive testing.

Explanation:
Understanding the business process is the first step an IS auditor needs to perform. Standards do not require
an IS auditor to perform a process walk through. Identifying control weaknesses is not the primary reason for
the walk through and typically occurs at a later stage in the audit, while planning for substantive testing is
performed at a later stage in the audit.