After properly configuring multiple VLANs， an administrator has decided to secure its VLAN network. Which three steps are required to secure this environment？ （Choose three.）（）
- A If a port is connected to a foreign device make sure to disable CDP， DTP， RPR， PAgP， UDLP， and any other unnecessary protocols， and enable UplinkFast/BPDU guard on it.
- B Enable root guard feature to prevent a directly or indirectly connected STP-capable device from affecting the location of the root bridge.
- C Configure VTP domains appropriately or turn off VTP altogether to limit or prevent possible undesirable protocol interaction with regards to the network-wide VLAN configuration.
- D Set the native VLAN ID to match the port VLAN ID of any 802.1q trunk to prevent spoofing.
- E Disable all unused ports and place them in an unused VLAN to avoid unauthorized access.