Mexico and Panama
No body of water separates the US. from Mexico
the Plateau of Tibet
Coastal Plain
Lake Erie
That would be the Rio Grande river.
Alps
The Rio Grande
Yes it is considered a landform. It is a small body of ocean that separates two landforms, namely Asia and North America.
Mainland Mexico, as well as the southwestern US, specifically southern California, Arizona, New Mexico and southern Texas.
Appalachian Mountains
Cancun is a city in Mexico.