lǎo / shī / zài / shè / yǐng / shǐ / kè / shàng / jiè / shào / le / àn / xiá / de / gōng / zuò / yuán / lǐ老师在摄影史课上介绍了暗匣的工作原理。The teacher explained how the camera obscura worked in the photography history class.