3 sentences

1. 班长向士兵们喊道：“立正！”

   bān​zhǎng xiàng shì​bīng men hǎn​dào:“ lì​zhèng!”

   The squad leader shouted to the soldiers, 'Attention!'

   Source: Dong Chinese Dictionary

2. 听到教官的口令后，操场上的士兵们迅速由立正转为稍息。

   tīng​dào jiào​guān de kǒu​lìng hòu, cāo​chǎng shàng de shì​bīng men xùn​sù yóu lì​zhèng zhuǎn​wéi shào​xī.

   Upon hearing the drill instructor's command, the soldiers on the field quickly shifted from attention to at ease.

   Source: Dong Chinese Dictionary

3. 学生们在操场上立正站好。

   xué​sheng men zài cāo​chǎng shàng lì​zhèng zhàn​hǎo.

   The students stood at attention on the playground.

   Source: Dong Chinese Dictionary