all of the above;
they had food shortages because they werent producing enough to keep up with the evergrowing population. thus leading to inflation because supply and demand.
the empire was too large to govern, hence leading to the overthrow by the germanic leader Odoacer.
communication was difficult because everything was done by foot and because it was so big, it was difficult to do.
to go witht the lack of communication because of the size of rome, the governments productivity fell because of the simple fact that it was huge.
hope this helped!