In a collapsed core design, which two layers are combined?

In a collapsed core design, the core and distribution layers are combined into a single layer. This design is common in smaller to medium-sized networks where the full three-tier hierarchical model (access, distribution, core) is not necessary. Combining these layers reduces complexity and cost by requiring fewer devices and interconnections, while still providing a high-speed backbone for the network. The other options are incorrect because: access and WAN: The access layer connects end devices, and the WAN (Wide Area Network) connects geographically dispersed networks; these are distinct functions. distribution and access: While these layers are adjacent in a three-tier model, they are not typically combined in a "collapsed core" design; rather, the core and distribution are. core and WAN: The core provides high-speed switching within the local network, and the WAN connects to external networks; these are separate architectural concerns.