Cisco IDS sensors form the eyes and ears of your Cisco network intrusion detection system. Placing sensors correctly throughout your network is crucial to successfully implementing your Cisco intrusion detection system . Where can an IPS sensor be placed in an enterprise network？（）
- A core layer
- B bridging two VLANs on one switch
- C between two Layer 2 devices with trunking
- D between two Layer 2 devices without trunking