When a client decides not to implement recommended process improvements from a consulting engagement, the internal audit activity should confirm the decision with management and document it in the audit file. This approach ensures that the audit trail is complete and that there is a record of management's acceptance of the associated risks. Escalating the issue to the board (Option A) or initiating an assurance engagement (Option D) might be necessary if the risks are significant, but these actions are not the immediate next steps. Continuous follow-up (Option C) is more relevant to assurance engagements rather than consulting engagements.
Reference:
IIA Standard 2500: Monitoring Progress.
IIA Practice Guide on Consulting Engagements.