The correct answer is C. Hilly areas.
Landslides are a potential hazard in hilly areas because of the steep slopes and loose soil. The heavy rains that Telangana experiences during the monsoon season can cause landslides, especially in areas that have been deforested.
Option A is incorrect because coastal areas are not prone to landslides. The soil in coastal areas is usually sandy and well-drained, which makes it less likely to slide.
Option B is incorrect because the northern plains are not as hilly as the southern part of Telangana. The northern plains are also more densely populated, which means that there are more people and infrastructure at risk from landslides.
Option D is incorrect because the Deccan plateau is a relatively flat area. The soil on the Deccan plateau is also more compacted than the soil in hilly areas, which makes it less likely to slide.