You are presented with the question "How does water cause a valley to form?" and the following answer choices: 
- Physical weathering
 - By the process of erosion
 - By falling from clouds
 - It used to be covered by water
 - fissures of hot, acidic water
 - Heavy snow accumulation
 - By forming puddles
 - Water expanding

Now knowing that avalley is formed by a river flowing and fast flowing rivers tend to pick up more pebbles, sand and other materials that cause erosion, choose the best answer.


 

  By the process of erosion       