Loop guard and UniDirectional Link Detection both protect against Layer 2 STP loops. In which two ways does loop guard differ from UDLD in loop detection and prevention？（）

• A、Loop guard can be used with root guard simultaneously on the same port on the same VLAN while UDLD cannot.
• B、UDLD protects against STP failures caused by cabling problems that create one-way links.
• C、Loop guard detects and protects against duplicate packets being received and transmitted on different ports.
• D、UDLD protects against unidirectional cabling problems on copper and fiber media.
• E、Loop guard protects against STP failures caused by problems that result in the loss of BPDUs from a designated switch port.