lì / shǐ / kè / shàng / lǎo / shī / xiáng / xì / jiè / shào / le / yī / èr / bā / shì / biàn / de / bèi / jǐng

历史课上，老师详细介绍了一二八事变的背景。

In history class, the teacher explained the background of the January 28 Incident in detail.