Lǎo / shī / xiān / jiǎng / jiě / píng / fāng / gēn / de / gài / niàn， / zài / dài / wǒ / men / zuò / tí。

老师先讲解平方根的概念，再带我们做题。

The teacher first explained the concept of square roots and then guided us through some exercises.