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to work (for); to be employed (at); to serve (in)
to serve (as); to act (as); to fill (the position of); to play the role (of)
to conduct a religious service
彼は十年間、社長を務めてきました。
He has served as company president for ten years.
結婚式で司会を務めることになった。
I ended up serving as the MC at the wedding.
このプロジェクトでリーダーを務めます。
I will serve as the leader in this project.