user
black we are and much addmired, men seek for us if they are tiered.  we tire the horses and confort the man, tell me this riddle if you can. 
A: coal
B: onions
C: carbon black
D: fireplace
E: marmoset
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

A

<|end_of_solution|>