Tropical grasslands, also known as savannahs, are characterized by a vast expanse of grasses with scattered trees and shrubs. They are found in regions of the world that have a tropical climate, typically located on or near the equator. The correct answer to the question is option 'B' - Savannah.

Factors that define tropical grasslands:

1. Climate: Tropical grasslands have a distinct wet and dry season. The average temperature is high throughout the year, and there is a relatively even distribution of rainfall.

2. Vegetation: Grasses are the dominant plant species in tropical grasslands, with a variety of species adapted to the seasonal changes in rainfall. Trees and shrubs are scattered, rather than forming dense forests.

3. Wildlife: Tropical grasslands support a diverse range of wildlife, including large herbivores such as elephants, giraffes, and zebras. Predators like lions, cheetahs, and hyenas are also found in these regions.

Examples of tropical grasslands:

a) Taiga: Taiga, also known as boreal forests, is a biome characterized by coniferous forests found in high-latitude regions, such as Canada, Russia, and Scandinavia. It is not a tropical grassland.

b) Savannah: Savannahs are the classic example of tropical grasslands. They are found in Africa, South America, Australia, and India, among other regions. The African savannah, often associated with iconic wildlife such as lions and elephants, is one of the most well-known examples.

c) Pampas: Pampas are grasslands found in South America, primarily in Argentina and Uruguay. They are characterized by fertile soil and are used for agriculture, particularly for cattle grazing. However, Pampas are not tropical grasslands; they are temperate grasslands.

d) Prairies: Prairies are grasslands found in North America, particularly in the central United States and Canada. They experience a temperate climate and are mainly used for agriculture. Prairies are also not tropical grasslands.

Conclusion:

Tropical grasslands, or savannahs, are characterized by a tropical climate, dominant grass vegetation, and a diverse range of wildlife. Examples of tropical grasslands include the African savannah, South American cerrado, Australian tropical savannah, and Indian subcontinent. Taiga, pampas, and prairies are not tropical grasslands, as they have different climate and vegetation characteristics.