lǎo shī / bǎ / yí gè / léng tái / mó xíng / fàng zài / jiǎng tái shàng / dài / dà jiā / guān chá / tā de / dǐ miàn / hé / cè miàn

老师把一个棱台模型放在讲台上，带大家观察它的底面和侧面。

The teacher placed a frustum model on the lectern and guided the class in observing its bases and sides.