The great plain, stretches across croatia, serbia, and romania and is highly populated because its fertile soil.

Hungarian

Explanation :

The Great Hungarian Plane which in Hungarian is known as Alfold, occupies most of the Hungary, about 56% of its area. It stretches across the following countries:

The soil is fertile because of the rivers that pass through the plane. River Tisza is the most prominent river of the plane

the wrong statement is - c. a desert had more biodiversity than a marsh.

the deserts are one of the places of the planet where there's the least biodiversity. the reasons for that are the climate and the lack of food sources, which hampers both the number of the species that can survive in it, and the number of the individuals in the species itself.

the marshes, on the other hand, are places where there's perfect conditions for lots of organisms to thrive. the temperature is moderate and nice, the amount of water and the food sources are on a high level, so there's an abundance of both plant and animal life in them.