Answer:
Located off the southeastern coast of North America
? - Caribbean islands
The caribbean Islands are immediately off the coast of southeastern coast of North America. The largest of them, Cuba, is only 103 miles away from Florida.
Mid-Atlantic - Most densely populated region of North America
The Mid-Atlantic includes the urban region from New York to Washington D.C, what is considered to some geographers as the "Mid-Atlantic megalopolis".
Midwest - Major agricultural producer in the United States
Most of the Midwest is flat, and very fertile, for this reason, Midwest states like Illinois and Iowa, are major agricultural producers of important crops like corn and wheat.
Pacific Northwest - Vast forests and active volcanoes, in the United States?
The Pacific Northwest is characterized by the mountain ranges that cross it. These mountains are very forested and some of them have active volcanoes, like Mount Rainier in Washington state.