Correct Option: A. Depositing Explanation of the Correct Answer When the gradient of a river channel changes from a steep to a gentle angle, the river's energy and velocity decrease. This change in gradient affects how the river interacts with the sediment it carries. Here’s a step-by-step breakdown of why the correct answer is "A. depositing":

1. Understanding River Dynamics:
2. Rivers are dynamic systems that transport water and sediment. The energy of the river is highest in steep areas, where the water flows quickly and can carry larger particles.
3. As the river flows into a gentler gradient, the velocity of the water decreases. This reduction in speed means the river can no longer carry as much sediment.
4. Sediment Transport:
5. Rivers transport sediment in three main ways: suspension (small particles carried within the water), saltation (larger particles bouncing along the riverbed), and traction (the rolling of large boulders along the bottom).
6. When the river slows down due to a gentler gradient, it loses the energy required to keep these sediments suspended or moving.
7. Deposition Process:
8. As the river's velocity decreases, it begins to deposit the sediment it has been carrying. This process is known as sediment deposition.
9. The larger and heavier particles are deposited first, followed by finer materials as the flow continues to slow down. This can lead to the formation of features such as river deltas, bars, and floodplains.
10. Geological Implications:
11. The areas where deposition occurs can lead to the creation of new landforms and habitats. For example, deltas form at the mouth of rivers where they meet larger bodies of water, and these areas are often rich in biodiversity.

Explanation of Why Other Options Are Incorrect

• B. Eroding:
• Erosion occurs when the river has enough energy to wear away the banks and bed of the river channel. In a steep gradient, the river has the energy to erode, but as it transitions to a gentler slope, the energy decreases, making erosion less likely. Therefore, this option is incorrect.
• C. Deepening:
• Deepening refers to the process of a river channel becoming deeper, which typically occurs in areas of high energy and steep gradients where erosion is dominant. In a gentle gradient, the river is more likely to deposit sediment rather than deepen its channel. Thus, this option is also incorrect.
• D. Terracing:
• Terracing is a process that involves the formation of step-like landforms along the sides of a river valley, often due to erosion and sediment deposition over time. While it can occur in river systems, it is not the primary activity when a river transitions from a steep to a gentle gradient. Therefore, this option is not the best answer.

Summary of Key Points

• When a river's gradient changes from steep to gentle, its velocity decreases.
• The decrease in velocity leads to sediment deposition, as the river can no longer carry the sediment it has transported.
• Erosion, deepening, and terracing are not the primary activities in this scenario due to the reduced energy of the river.
• Understanding river dynamics is crucial for predicting sediment transport and deposition patterns.

This thorough understanding of river behavior will help you in your geography studies and in answering similar questions in your exams.