I am having problems with the correct use of the subject-verb agreement. Here
is an example of one of my assignments:

"One of the world's oldest and most famous newspaper centers (are/is) Fleet
Street. This area, with its hundreds of alleys, (run/ran) like a crooked
spine through east-central London. Here (are/is) published almost all of
Britain's national newspapers. In no other country (are/is) a nation's
newspapers centered in once location."

English has never been one of my strong points. Can someone please help me
with an easy way to remember the rule? Please help!! Thank you so much.

Faithsmimi