user
I can be quick and then I'm deadly,  I am a rock, shell and bone medley.   If I was made into a man, I'd make people dream,  I gather in my millions by ocean, sea and stream. 
A: sand
B: flounders
C: black and white
D: sign
E: white man
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

A

<|end_of_solution|>