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self-study; teaching oneself
studying by oneself (at school) while the teacher is absent
自習の時間を使って宿題を終わらせることにした。
I decided to use self-study time to finish my homework.
自習室は静かで勉強に集中できる環境だと思う。
I think the self-study room is quiet and a good environment to concentrate.
放課後は図書室で自習するのが習慣だ。
It's my habit to study on my own in the library after school.