Which aspect must be the part of the design to mitigate the risk of connectivity issues between the data centers?

As part of network design, two geographically separated data centers must be interconnected using Ethernet-over-MPLS pseudowire. The link between the sites is stable, the topology has no apparent loops, and the root bridges for the respective VLANs are stable and unchanging.

Which aspect must be the part of the design to mitigate the risk of connectivity issues between the data centers?
A . Enable 802.1d on one data center, and 802.1w on the other.
B . Ensure that the spanning tree diameter for one or more VLANs is not too large.
C . Enable UDLD on the link between the data centers.
D . Enable root guard on the link between the data centers.

Answer: B