Black Friday: lifetime access is on a special offer in the app, until November 30. Black Friday: special offer on lifetime access, until November 30. Download
호흡기계는 산소를 공급하는 중요한 역할을 합니다.hoheupgigeun sansoreul gongbuhaneun jungyohan yeoghal-eul hamnida.The respiratory system plays an important role in supplying oxygen.