The correct answers are C and D.
OBJ-2.5: Segmentation is the best method to reduce the risk to an embedded ICS system from a network-based compromise. Additionally, you could disable unused services to reduce the footprint of the embedded ICS. Many of these embedded ICS systems have a large number of default services running. So, by disabling the unused services, we can better secure these devices. By segmenting the devices off the main portion of the network, we can also better protect them. A NIDS might detect an attack or compromise, but it would not reduce the risk of the attack succeeding since it can only detect it. Patching is difficult for embedded ICS devices since they usually rely on customized software applications that rarely provide updates.