The Ethiopian Highlands is not part of the physiographic regions of North America.

Explanation:
The physiographic regions of North America refer to the different geographic areas that make up the continent. These regions are characterized by their distinct landforms, geological features, and topography. They help in understanding the diverse physical characteristics of North America.

The Ethiopian Highlands, however, are not part of North America. They are a mountainous region located in eastern Africa, primarily in Ethiopia. This region is known for its high elevations, rugged terrain, and unique biodiversity. The Ethiopian Highlands are not connected to North America geographically or geologically.

On the other hand, the other options mentioned in the question are all part of the physiographic regions of North America. Let's briefly discuss each of them:

a) Canadian Shield: The Canadian Shield is a large geological formation that covers a significant portion of Canada. It is one of the oldest rock formations on Earth and is characterized by its exposed bedrock, numerous lakes, and boreal forests. The Canadian Shield is located in the northeastern part of North America.

b) Appalachian Mountains: The Appalachian Mountains are a major mountain range in eastern North America. They extend from Newfoundland and Labrador in Canada, through the northeastern United States, and down to northern Alabama in the southern United States. The Appalachian Mountains are known for their scenic beauty, diverse flora and fauna, and rich cultural history.

c) Atlantic Coastal Plain: The Atlantic Coastal Plain is a low-lying region along the eastern coast of North America, stretching from New England in the north to Florida in the south. It is characterized by its flat topography, sandy beaches, and extensive wetlands. The Atlantic Coastal Plain is an important agricultural and industrial region in North America.

In conclusion, the Ethiopian Highlands are not part of the physiographic regions of North America. They are located in eastern Africa, while the other options mentioned (Canadian Shield, Appalachian Mountains, and Atlantic Coastal Plain) are all part of the physiography of North America.