Where would a business man keep a plane ticket with other documents?
Options:
- briefcase
- boarding plane
- airport
- pocket
- shirt sleeve
Please answer and provide answer explanation.

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
Businessmen end to carry briefcases. They keep important documents in the briefcase. Plane ticket is an important document. The final answer: briefcase.