constantly flowing water many fish in the river new soil deposited by the river warm water from an ocean
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: What causes the soil in a flood plain to be generally rich in nutrients?
Possibilities:
- constantly flowing water
- many fish in the river
- new soil deposited by the river
- warm water from an ocean

new soil deposited by the river