Lì / shǐ / kè / shàng / lǎo / shī / jiè / shào / le / Bō / cí / tǎn / gōng / gào / de / bèi / jǐng

历史课上，老师介绍了波茨坦公告的背景。

In history class, the teacher explained the background of the Potsdam Declaration.