The correct answer is: C. rocks, weathering.
Weathering is the process by which rocks are broken down into smaller pieces. This can happen through physical weathering, such as when rocks are broken down by wind or water, or chemical weathering, such as when rocks are dissolved by acids. The products of weathering, such as sand and gravel, are a major source of sediments for erosion. Erosion is the process by which sediments are moved from one place to another, usually by wind or water.
Option A is incorrect because deposition is the process by which sediments are deposited, not the process by which they are formed. Option B is incorrect because weathering is the process by which rocks are broken down, not the process by which they are deposited. Option D is incorrect because rocks are not the only source of sediments for erosion. Sediments can also be formed from the remains of plants and animals.