Task: Sentence Ordering
Input (English): Steps: (1) A large rocky area is formed (2) The rocky area has a higher elevation than the surrounding areas (3) Water from precipitation falls in the area (4) The water forms a stream (5) The stream flows towards lower elevation (6) The river continues to flow along the same path for a long time (7) The river erodes the rocky area that it touches (8) The eroded area cuts deeply into the rock.  
Where does the following step fit into the given list of steps: The stream becomes a river 
Output (English):  After step 5.