Concept:A youthful river is in its upper course and actively erodes its channel downwards through the landscape.
Explanation:The youthful stage of a river is marked by steep gradients and high erosive power.
The river cuts downward into the land, forming steep-sided V-shaped valleys, rapids, waterfalls, and interlocking spurs.
Features like levees, deltas, and oxbow lakes develop later in a river's course.
Levees and deltas appear in the lower course, while oxbow lakes form in the mature stage.
Therefore, the feature that is commonly found in the youthful stage is an interlocking spur.
Answer:D. Interlocking spur