Refer to the exhibit.

A multilayer switch has been configured to send and receive encapsulated and tagged frames. VLAN 2013 on the multilayer switch is configured as the native
VLAN. Which option is the cause of the spanning-tree error?

A.
VLAN spanning-tree in SW-2 is configured.

B.
spanning-tree bpdu-filter is enabled.

C.
802.1q trunks are on both sides, both with native VLAN mismatch.

D.
VLAN ID 1 should not be used for management traffic because its unsafe.

Explanation:
Here we see that the native VLAN has been configured as 2013 on one switch, but 1 (the default native VLAN) on the other switch. If you use 802.1Q trunks, you
must ensure that you choose a common native VLAN for each port in the trunk. Failure to do this causes Cisco switches to partially shut down the trunk port
because having mismatched native VLANs can result in spanning-tree loops. Native VLAN mismatches are detected via spanning tree and Cisco Discovery
Protocol (CDP), not via DTP messages. If spanning tree detects a native VLAN mismatch, spanning tree blocks local native VLAN traffic and the remote switch
native VLAN traffic on the trunk; however, the trunk still remains up for other VLANs.

http://www.informit.com/library/content.aspx?b=CCNP_Studies_Switching&seqNum=25