What describes how the 802.1Q protocol lactates the transmission of multiple Layer 2 networks on a single link?

What describes how the 802.1Q protocol lactates the transmission of multiple Layer 2 networks on a single link?
A . adds 802.1Q tag information between the source MAC address and the Ether Type/Length fields
B . encapsulates the frame inside an 802.1Q tunnel
C . adds 802.1Q tag information between the preamble and the destination MAC address
D . encapsulates the packet inside an 802.1Q tunnel
E . transparently directs packets based on 802.1Q tags inside the header

Answer: A

Explanation:

EEE 802.1Q uses an internal tagging mechanism which inserts a 4-byte tag field in the original Ethernet frame itself between the Source Address and Type/Length fields http://www.cisco.com/c/en/us/support/docs/lan-switching/8021q/17056-741-4.html#topic2