The correct answer is: a) At high altitudes.
The Western Ghats are a mountain range in India that runs along the western coast of the country. They are home to a variety of plant and animal life, including many species that are found nowhere else in the world. The Western Ghats are also home to a number of montane grasslands, which are grasslands that are found at high altitudes. These grasslands are typically characterized by their short, dense grass and their lack of trees. The montane grasslands of the Western Ghats are an important habitat for a number of species of birds, mammals, and reptiles.
Option b) is incorrect because valleys are typically found at lower altitudes than montane grasslands.
Option c) is incorrect because southern slopes are not necessarily higher in altitude than northern slopes.
Option d) is incorrect because montane grasslands are not typically found near rivers.