Final answer:
The correct ecoregion found in Texas from the provided options is the Panhandle Plains.
Step-by-step explanation:
The ecoregion found in Texas that matches the options provided is d. Panhandle Plains. Texas features a variety of ecoregions, but tropical rainforests, mangrove country, and tundra are not among them. While Texas does have diverse ecosystems, the Panhandle Plains is the only option listed that accurately represents an ecoregion of Texas. This ecoregion is characterized by its flat grassland areas, which are largely used for agriculture today. In contrast, tropical rainforests and mangroves are not representative of Texas's ecosystems, and tundra is a biome found in much colder regions, typically closer to the poles.