Final answer:
The external auditor is least likely to participate in a system's study since their role is focused on auditing financial statements independently, unlike internal auditors, top managers, and IT department members who are involved with internal system processes and improvements.
Step-by-step explanation:
The individual who is least likely to participate in a system's study is typically the external auditor. An external auditor's main role is to provide an independent opinion on an organization's financial statements, not to be involved in the internal workings or system improvements of the company they are auditing.
On the other hand, an internal auditor, a top manager, and a member of the IT department all have roles that inherently involve assessing, managing or directly working with the company’s systems and processes.
An internal auditor evaluates internal controls and risks, a top manager makes strategic decisions including those concerning systems, and IT department personnel are responsible for implementing and maintaining technological systems.