How can a user view an X Window from a remote system on their local system?

How can a user view an X Window from a remote system on their local system?

A.
from the local system:
export DISPLAY=remote:0.0

B.
from the remote system:
export DISPLAY=remote:0.0

C.
from the local system:
export DISPLAY=local:0.0

D.
from the remote system:
export DISPLAY=local:0.0