1 sentence for 闭门 (bì​mén — close door)

1. 他虽然只是一名增生，但依然坚持闭门苦读。

   tā suī​rán zhǐ shì yī míng zēng​shēng, dàn yī​rán jiān​chí bì​mén kǔ​dú.

   Although he was only a supplementary student, he still persisted in studying hard behind closed doors.

   Source: Dong Chinese Dictionary