Which geographical area is described as making up the eastern part of the lower half of a state, bordering the Atlantic Ocean?

The Atlantic Coastal Plain is the correct answer because it refers to a geographic region that extends along the eastern coast of the United States and is characterized by its low-lying flat land that directly borders the Atlantic Ocean. This area typically includes coastal cities and is known for its distinct ecosystems and economic activities, such as fishing and tourism.

In terms of the other choices, the Appalachian Mountains are a major mountain range located further inland, running from the northeastern to the southeastern United States, and do not border the Atlantic Ocean in the way described. The Great Plains are a vast expanse of flat land located in the central United States, known for agriculture and grasslands, but they are not in the southeastern part of any state. Lastly, the Rocky Mountains are a significant mountain range located in the western United States, far from the eastern coastal regions. Thus, the Atlantic Coastal Plain is accurately defined by its geographical location and characteristics in relation to the Atlantic Ocean.