Which single design aspect should be configured on the ABRs to reduce the impact of WAN upgrades for spoke routers on the core of the network?

Refer to the exhibit.

Which single design aspect should be configured on the ABRs to reduce the impact of WAN
upgrades for spoke routers on the core of the network?

A.
route summarization

B.
stub area

C.
route filtering

D.
not-so-stubby area