If the OSPF protocol is used to connect customer edge （CE） routers to service provider edge（PE） routers in the VPN backbone， which two options best describe the use of SHAM links？（）

A sham-link is created between any twoo VPN sites that belong to the same OSPF area and share an OSPF backdoor link
B. A sham-link is seen as an intra-area link between PE routers，an OSPF adjacency is created and data base is exchanged
C. A SHAM link is created between two directly connected PE routers so that it is preferred over the low speed backdoor door
D. A SHAM link is part of OSPF network of MPLS-VPN provider