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third-year student; third-year pupil
三さん年ねん生せいの学生がくせい。
A third-year student.
三さん年ねん生せいは来年らいねん卒業そつぎょうする。
Third-year students will graduate next year.
彼かれは三さん年ねん生せいになったばかりだ。
He just became a third-year student.