If an Ethernet data frame is Length/type=0x8100, which of the following statements is correct?

If an Ethernet data frame is Length/type=0x8100, which of the following statements is correct?
A . There must be a UDP header in the upper layer of this data frame
B . There must be a TCP header in the upper layer of this data frame
C . This data frame must carry vlan TAG
D . There must be an IP header in the upper layer of this data frame

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Answer: C