Xiào / zhǎng / zǒu / jìn / huì / chǎng / hòu， / suǒ / yǒu / xué / sheng / lì / kè / zhèng / jīn / wēi / zuò。

校长走进会场后，所有学生立刻正襟危坐。

After the principal entered the hall, all the students immediately sat upright and still.