The correct answer is B — Wireless intrusion prevention system (WIPS).

According to WGU Cybersecurity Architecture and Engineering (KFO1 / D488), a WIPS actively monitors wireless networks for unauthorized access points and malicious activity, such as man-in-the-middle (MITM) attacks. It can automatically detect, alert, and prevent wireless threats in real time, which is exactly what the organization requires to counteract MITM attacks on the wireless network.

A SIEM (A) collects logs and generates alerts but does not prevent wireless attacks. An inline encryptor (C) encrypts data but does not prevent wireless attacks. A Layer 3 switch (D) operates at the network layer and does not prevent wireless-specific threats.

Reference Extract from Study Guide:

"A wireless intrusion prevention system (WIPS) detects and prevents unauthorized access points and malicious wireless activity, including man-in-the-middle attacks."

— WGU Cybersecurity Architecture and Engineering (KFO1 / D488), Wireless Security and Threat Prevention

=============================================