Fact 1: Erosion causes a river to become deeper and wider. Fact 2: Less soil is lost to erosion. Given the two facts above, what loss causes a river to become deeper and wider?

Select from:
[1]. cut.
[2]. fish.
[3]. rain.
[4]. storms.
[5]. eroded.
[6]. water.
[7]. habitat.
[8]. soil.
The answer is:
[8].