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
몬트리올 의정서는 오존층 보호를 위한 국제 협약입니다.Montreal uijeongseoneun ojongcheung bohoreul wihan gukje hyeobagimnida.The Montreal Protocol is an international agreement to protect the ozone layer.