When executing the following show mpls l2transport vc detail command, you notice the link does not come up. Choose the most likely cause.

PE#sho mpls l2transport vc detail
Local interface: Et0/0 up, line protocol up, Ethernet up
Destination address: 172.168.1.102, VC ID: 100, VC status: down Preferred path: not configured
Default path: active
Tunnel label: 16, next hop point2point
Output interface: Se5/0, imposed label stack {16 16}
Create time: 00:18:10, last status change time: 00:03:51
Signaling protocol: LDP, peer 172.168.1.102:0 up
MPLS VC labels: local 16, remote 16
Group ID: local 0, remote 0
MTU: local 1500, remote unknown
Remote interface description:

Sequencing: receive disabled, send disabled
VC statistics:
packet totals: receive 0, send 0
byte totals: receive 0, send 0
packet drops: receive 0, send 78

A.
MPLS is not enable from PE to P.

B.
The remote PE interface is down.

C.
TDP is configured instead of LDP.

D.
There is a remote side MTU mismatch.