If a Side Stream Feeds Coarse Gravel into a River

Multiple Choice

If a side stream feeds coarse gravel into a river with a sandy bottom, what does the river do about it?

A) The river flushes it down into the valley.
B) The slope of the riverbed builds up until it is steep enough to transport the size of gravel supplied, or until a flood carries it downstream.
C) The gravel dams the river channel.
D) The gravel works down through sediments in the riverbed until it reaches bedrock.
E) The water slows down because the larger sediment gets in the way.