Which is a correct statement about bridge port roles in STP?

A. A designated port is always in a blocking state.
B. Every switch, including the root bridge, must have at least one designated port.
C. Every switch, excluding the root bridge, must have at least one nondesignated port.
D. All ports on the root bridge are in a designated port state.

D. The root bridge always has all of its ports in a designated mode or forwarding mode. If there are redundant links, the adjacent switch to the designated port on the root bridge must be a non-designated or blocking state.