The natural boundary that extends 20,000 square miles and separates spain and portugal from the rest of europe is the a. northern european plain b. pyrenees mountains c. iberian peninsula d. british isles

B. Pyrenees Mountains

Explanation:

This natural boundary is the Pyrenees. The Pyrenees is a range of mountains in Europe that forms the natural border between Spain and France. It also separates the Iberian Peninsula from the rest of Europe. The microstate of Andorra is also located in this region, in between the two nations. Some historical regions have occupied both sides of the border, such as the Principality of Catalonia, the Kingdom of Aragon and the Kingdom of Navarre. Most of these historical areas are now located within Spain.