which layer in a tiered data center architecture ?

A hardware-based gateway that provides for spanning application workloads across virtual and physical spaces will most likely be installed at which layer in a tiered
data center architecture ?

A.
An access layer, top of the rack switch (TOR).

B.
A distribution services layer, end of the row switch (EOR).

C.
In a collapsed distribution and core layer.

D.
Any layer within a multi-tiered data center architecture.