Threat hunting is a proactive security activity focused on identifying hidden or undetected threats within an environment, even when no alerts or indicators have been triggered. According to CompTIA Security+ SY0-
701, threat hunting assumes that attackers may already be present and actively evading traditional security controls such as SIEMs, IDS/IPS, or endpoint protection tools.
Threat hunting involves manually analyzing logs, endpoint telemetry, network traffic, and behavioral patterns to uncover anomalies that automated systems may miss. This aligns directly with the scenario, where the analyst has a suspicion of malicious actors but no alerts confirming activity. Threat hunting helps identify advanced persistent threats (APTs), living-off-the-land techniques, credential misuse, and lateral movement that may not generate immediate alerts.
Digital forensics (B) is typically performed after an incident has been confirmed. Vulnerability scanning (C) identifies weaknesses but does not detect active attackers. E-discovery (D) is a legal process for collecting electronically stored information and is not used for threat detection.
Because the analyst is proactively searching for hidden threats without existing alerts, the correct action is A:
Threat hunting.

An intrusion prevention system (IPS) is a security device that monitors network traffic and blocks or modifies malicious packets based on predefined rules or signatures. An IPS can prevent attacks that exploit known vulnerabilities in older browser versions by detecting and dropping the malicious packets before they reach the target system. An IPS can also perform other functions, such as rate limiting, encryption, or redirection. References: CompTIA Security+ Study Guide: Exam SY0-701, 9th Edition, Chapter 3: Securing Networks, page 132.

Firewalls are classic examples of technical controls as they use technology to restrict or permit network traffic based on security policies. Technical controls are implemented through hardware or software solutions.
Security guards (A) and fences (C) are physical controls, while policies (B) are administrative controls.
Technical controls like firewalls are fundamental in securing network perimeters and endpoints as covered in the Security Architecture domain#6:Chapter 3 CompTIA Security+ Study Guide#.

Management review is a critical step in the change management process. Before implementing any design change, management reviews help evaluate the potential impact, security implications, and alignment with organizational goals and policies. This review ensures that the change is justified, risks are understood, and proper approvals are obtained.
Load testing is a performance test, maintenance notifications are communication steps, and procedure updates are documentation activities - all important but generally occur after management has approved the change.
The significance of management involvement in change governance is a foundational concept in the Security Program Management and Oversight domain of the SY0-701 exam#6:Chapter 16 CompTIA Security+ Study Guide#.

A Certificate Signing Request (CSR) is a request sent to a certificate authority (CA) to issue an SSL certificate. The CSR contains information like the public key, which will be part of the certificate.References:
Security+ SY0-701 Course Content, Security+ SY0-601 Book.