In the Figure Below,why Would the Densest Clasts Probably Be

Multiple Choice

In the figure below,why would the densest clasts probably be at the bottom of the river channel?

A) Denser clasts are larger and are therefore found at the river bottom.
B) Denser clasts roll (due to landslides, etc.) further into the river and so are most common in the middle of the channel.
C) Denser clasts require more energy to move and so are deposited first, into flood-scoured channels when waters begin to slow.
D) Denser clasts are more magnetic and weak molecular forces cause them to "stick" to water molecules.