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
시대론은 사회 변화의 원인을 설명하는 데 사용됩니다.sidaeron-eun sahoe byeonhwa-ui wonin-eul seolmyeonghaneun de sayongdoemnida.The theory of the era is used to explain the causes of social change.