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
철도에서 침목은 기차의 안전한 운행을 위해 필수적이다.cheoldoeso chimok-eun gicha-ui anjeonhan unhaeng-eul wihae pil-su-jeogida.In railways, crossties are essential for the safe operation of trains.