Lìshǐ / kè / shàng / lǎoshī / jièshào / le / bǎohùguó / zhìdù / de / xíngchéng / hé / biànhuà

历史课上，老师介绍了保护国制度的形成和变化。

In history class, the teacher introduced the formation and development of the protectorate system.