The answer would be The rainforest.
The desert is a dry place that has little to no water so this wouldn’t be the correct answer.
The tundra isn’t as dry as the desert and is mostly an open space with big mountains.
The plains are wide open areas of flat land and is mostly grassland.
The rainforest however is full of trees and rains their daily. It isn’t full of animals and wildlife. Compared to the other options this would be correct since it is also called the tropical rainforest.
Hope this helps! :3