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
금속의 패시베이션은 부식을 방지하는 데 중요하다.geumsogeui paesibeisyeoneun busigeul bangjihaneun de jungyohada.The passivation of metals is important for preventing corrosion.