Fact 1: Erosion causes a river to become deeper and wider. Fact 2: Fertile topsoil is then lost in erosion. Given the two facts above, deepening rivers cause?

OPTIONS: 1. relocation; 2. the loss of topsoil; 3. Plant growth is reduced; 4. to move people; 5. Physical weathering; 6. forest is destroyed; 7. Water expanding; 8. water conservation;
The answer is:
2.