user
what could nevr fly up and never fly down, but go side to side?
A: airplanes
B: plane
C: movement
D: human being
E: planes
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

D

<|end_of_solution|>