Why Are the Deposits of Streams Graded with the Largest

Multiple Choice

Why are the deposits of streams graded with the largest boulders or pebbles at the bottom?

A) The largest boulders are always at the bottom; they never move.
B) The largest boulders eroded from the stream bank immediately roll to the bottom and stay there.
C) Jostling of boulders, pebbles, and sand in turbulent water moves the boulders to the bottom.
D) As the water slows after a flood, the largest boulders drop out first.
E) Tributaries add additional sediment to the stream.