Question

which plains stretch from hungary to croatia, serbia, and romania? balkan plains great hungarian plains northern european plains

Explanation:

The Great Hungarian Plains (also known as the Pannonian Plain) extends from Hungary into Croatia, Serbia, and Romania. The Balkan Plains are more focused on the Balkan Peninsula's southern regions, and the Northern European Plains are in more northern European areas (e.g., through Germany, Poland), not matching the described region.

Answer:

B. Great Hungarian Plains