Rivers downcutting into a land surface, in the absence of other forces, usually tend to erode a -shaped form when viewed in cross-section across its valley. flat bottomed U delta V groove

Rivers downcutting into a land surface, in the absence of other forces, usually tend to erode a V-shaped form when viewed in cross-section across its valley.

Explanation:

Rivers on steep surfaces tend to have a very high flow speed and the higher the slope of the terrain and the speed of the river, the greater the erosion power of these rivers. Under these conditions, a river can deepen its bed, creating a V-shaped valley, especially at the headwaters of the banks, where the erosion process is usually greater.

d. they are naturallyoccuring inorganic fuels like coal and petroleum.