user
Dark with white markings, And smooth like a rock.  Where learning occurs, I help convey thought.  What am I?
A: thoth
B: pluto
C: blackboardchalkboard
D: gibraltar
E: urethane
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

C

<|end_of_solution|>