The correct answer is D because a warning banner is a deterrent control designed to discourage inappropriate or unauthorized activity. Deterrent controls do not necessarily prevent an action technically; instead, they warn users of consequences, establish notice, and reduce the likelihood of misuse. A warning banner may inform users that access is monitored, unauthorized access is prohibited, and violations may result in disciplinary or legal action. Separation of responsibilities is primarily a preventive control because it reduces the opportunity for fraud, error, or misuse by dividing duties among different individuals. Periodic data restoration is a corrective or recovery control because it helps restore data after loss or corruption. An intrusion detection system is a detective control because it identifies suspicious or unauthorized activity after it occurs or while it is occurring. CISM requires understanding the purpose of control types, including preventive, detective, corrective, deterrent, compensating, and recovery controls. Since a warning banner discourages undesirable behavior, it is the best example of a deterrent control.