Answer:
B. NIDS
Explanation:
From the question we are informed about A network manager is interested in a device that watches for threats on a network but does not act on its own, and also does not put a strain on client systems. The BEST device to meet these requirements is NIDS. Network intrusion detection system known as "NIDS" can be regarded as a system that can attempt in detection of hacking activities as well as denial of attack on computer network. It can monitor network traffic and can as well detect malicious activities through identification of suspicious patterns in any incoming packet.
