Explanation:

• Weathering is a precondition for erosion to take place: This statement is incorrect. By erosion, relief degrades, i.e., the landscape is worn down. That means, though weathering aids erosion it is not a pre-condition for erosion to take place. Weathering, mass-wasting and erosion are degradational processes.
• Karst topography is characterized by an underground drainage system: This statement is correct. Karst topography is formed by the dissolution of soluble rocks, such as limestone and gypsum, creating features like caves, sinkholes, and underground drainage systems.
• Glaciers are more effective as agents of erosion than wind: This statement is correct. Glaciers, due to their enormous size and mass, are more effective agents of erosion compared to wind. Glaciers can carve out valleys, fjords, and other large landforms through the process of glacial erosion.