organization of the petroleum exporting countries. (2017). annual report 2017. grasl druck & neue medien gmbh.
芝加哥风格引文organization of the petroleum exporting countries. Annual Report 2017. austria: grasl druck & neue medien gmbh, 2017.
MLA引文organization of the petroleum exporting countries. Annual Report 2017. grasl druck & neue medien gmbh, 2017.
警告：这些引文格式不一定是100％准确.