What was the question for this implicit rationale, and corresponding answer?
Sky is the region of upper air over the earth. Birds fly up in the air.
 The answer: sky

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
The question: The bird flies up in what?
Options:
- sky
- mountain
- forest
- nest
- roof