In trying to observe hacker techniques, a security administrator configures a nonproduction network to be applied as a target so that she can covertly monitor network attacks. What is this type of network called?

A honeynet is a decoy network that is set up to lure attackers in and observe their behavior. It is typically isolated from the production network and populated with simulated assets, such as servers, workstations, and data. Honeynets can be used to detect a wide range of attacks, including malware infections, unauthorized access attempts, and data exfiltration.
The other options are not correct:
Active detection is a general term for techniques that are used to detect security threats. Honeynets are one type of active detection technique.
A false subnet is a subnet that is configured to appear to be part of the production network but is actually isolated. It can be used to monitor traffic to and from the production network, but it cannot be used to observe attacker behavior in the same way as a honeynet.
An IDS (intrusion detection system) is a device or software that monitors network traffic for suspicious activity. IDS systems can be used to detect attacks that are already in progress, but they cannot be used to observe attacker techniques in the same way as a honeynet.