Which two of the following are characteristics of the campus layer hierarchy tiers ? (Choose two.)

A.
The network can have two tiers of switches combined into one

B.
Having three physical tiers is a strict requirment

C.
Each layer in a hiararchy can perform the functions of the other layers

D.
A network can have four or more physical tiers of switches, if necessery

E.
There are absolute rules fro how a campus networ is physically built