Refer to the exhibit. Customer XYZ is using an MPLS VPN to connect its locations of Site_A, Site_B, and Site_C. Each site uses OSPF as the CE-PE routing protocol. After a new direct 56 kbps link was added between Site_A and Site_B, all applications degraded in response time only between Site_A and Site_B. What is the most probable cause and its solution?
Exhibit:

A.
A routing loop needs to be corrected by an OSPF down bit.

B.
A routing loop needs to be corrected by the OSPF tag field.

C.
Suboptimal routing needs to be corrected by a virtual link.

D.
Suboptimal routing needs to be corrected by a sham link.