lǎo / shī / zài / lì / shǐ / kè / shàng / jiè / shào / le / hù / guó / jūn / fǎn / duì / Yuán / Shì / kǎi / de / bèi / jǐng

老师在历史课上介绍了护国军反对袁世凯的背景。

The teacher explained the background of the National Protection Army's opposition to Yuan Shikai in history class.