The correct answer is: c) Hilly areas.
Terrace cultivation is a farming technique used on steep slopes to create a series of flat, level terraces. This helps to reduce soil erosion and makes it easier to plant and harvest crops. Terrace cultivation is most common in hilly areas, where the land is naturally sloping.
Option a) River valleys are not typically used for terrace cultivation because the land is often too flat. Option b) Plains are also not typically used for terrace cultivation because the land is often too dry. Option d) Wetlands are not typically used for terrace cultivation because the land is often too wet.
Terrace cultivation is a sustainable farming technique that can help to improve crop yields and reduce soil erosion. It is a common practice in many parts of the world, including Asia, Africa, and South America.