There all correct...........
I believe the answer is B
When dead body parts decay.
<span>Downcutting (also known as rejuvenation) of a stream may be due to the uplift of land. It is a process by the action of the hydraulic that makes the channel of the valley or stream by simply get rid of any material on the floor of valleys and streams. Downcutting speed is determined by the base level of the stream. It is the lowermost point that a valley or streams can lose.</span>
