What is a function of the core and distribution layers in a collapsed-core architecture?

What is a function of the core and distribution layers in a collapsed-core architecture?

A. The router can support HSRP for Layer 2 redundancy in an IPv6 network. B. The core and distribution layers are deployed on two different devices to enable failover. C. The router operates on a single device or a redundant pair. D. The router must use IPv4 and IPv6 addresses at Layer 3.