where are the best places to place intrusion detection/intrusion prevention systems?

In keeping with the best practices of layered security, where are the best places to place intrusion
detection/intrusion prevention systems? (Choose two.)

A.
HID/HIP (Host-based Intrusion Detection/Host-based Intrusion Prevention)

B.
NID/NIP (Node-based Intrusion Detection/Node-based Intrusion Prevention)

C.
NID/NIP (Network-based Intrusion Detection/Network-based Intrusion Prevention)

D.
CID/CIP (Computer-based Intrusion Detection/Computer-based Intrusion Prevention)