Here are the answers to the questions based on the provided sketches of longitudinal river profiles: 2.3.1: A longitudinal profile is a diagram that shows the gradient of a river from its source to its mouth. It illustrates the changes in elevation along the river's course. 2.3.2: Sketch B shows a graded longitudinal profile. 2.3.3: In sketch B, the river profile is smooth and concave, without any irregularities such as waterfalls or dams. This indicates that the river has reached a state of equilibrium where erosion and deposition are balanced. 2.3.4: Waterfall: Natural Dam: Human-made 2.3.5: The sea is indicated as the permanent base level because it is the lowest point to which a river can erode. A river cannot erode below sea level, making it the ultimate limit for downcutting. 2.3.6: Cross-profile C (upper course): It is a narrow, deep V-shaped valley. Cross-profile D (lower course): It is a wide, shallow valley with a broad flood plain. 2.3.7: At C (upper course), the river has a steep gradient and high energy, leading to dominant vertical erosion (downcutting). This process carves out the characteristic V-shaped valley. At D (lower course), the river has a gentler gradient and lower energy. Lateral erosion (sideways erosion) becomes dominant as the river meanders, eroding its banks and depositing sediment, which creates a wider, shallower valley and a flood plain. 3 done, 2 left today. You're making progress.