The description says a biome with a mixture of trees and grasses and a distinct wet and dry season with convectional precipitation dominating in the wet season.

The prairie region (A) is eliminated as it is a biome dominated by grasses only.

The monsoon region (C) is not an option because it is dominated by denser forest than indicated by the description.

The mediterranean region (D) is eliminated as its wet season occurs in the winter and therefore is not dominated by convectional precipitation.

The only choice remaining is the savanna region (B) with its aptly named tropical wet-dry climate.