Which geographical area refers to the eastern part of the United States?

The eastern part of the United States is indeed defined as the area next to the Atlantic Ocean. This geographical placement is significant because it encompasses a variety of states and regions that are historically, culturally, and economically linked to the Atlantic. The coastline has played a crucial role in the development of many early American settlements and continues to influence trade, tourism, and transportation today.

The other options, while they may refer to important geographical regions, do not specifically define the eastern part of the United States. The area west of the Mississippi River generally refers to the western United States, the area north of the Great Lakes is associated more with the northern states, and the Gulf Coast region specifically pertains to states that border the Gulf of Mexico, which is not exclusively eastern. Thus, the correct identification of the eastern part of the United States corresponds to its proximity to the Atlantic Ocean.