user
I can be crystal clear But also pitch black.  people like me when i am as clear as the fresh air.  You can find me just about everywhere.  Besides the desert.  im very important to have.  any living thing can not live without me.  in very hot places im so desirable.  i come in jug containers or you can find me running through pipes.  What am i?
A: refractive index
B: bunker
C: discharge pipe
D: water
E: trial
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

D

<|end_of_solution|>