Usages of lǎoshī
你 是 老师 吗？nǐ shì lǎoshī ma?
Are you a teacher?
我 不 是 老师。wǒ bú shì lǎoshī.
I am not a teacher.
Note how bù (falling tone) changes it's pronunciation to bú (rising tone) when followed by a falling tone.
这 个 人 不 是 老师。zhè gè rén bú shì lǎoshī.
This person is not a teacher.
这 个 老师 在 家。zhè gè lǎoshī zài jiā.
This teacher is at home.
那 个 老师 今天 太 忙 了。nà gè lǎoshī jīntiān tài máng le.
That teacher is too busy today.
刚才 老师 给 我 发 了 邮件， 你 看 了 吗？Gāngcái lǎoshī gěi wǒ fā le yóujiàn, nǐ kàn le ma?
Just now the teacher sent me an email; did you see it?
老师 先 说 语法， 然后 让 我们 写 句子。lǎoshī xiān shuō yǔfǎ, ránhòu ràng wǒmen xiě jùzi.
The teacher first explains the grammar, then lets us write sentences.
老师 说 我们 得 好好 做 这些 练习。lǎoshī shuō wǒmen děi hǎohāo zuò zhèxiē liànxí.
The teacher said we must do these exercises carefully.
在 中文 课 上， 老师 让 我们 自由 说 中文， 表达 自己 的 意见。zài zhōngwén kè shàng, lǎoshī ràng wǒmen zìyóu shuō zhōngwén, biǎodá zìjǐ de yìjiàn.
In Chinese class, the teacher lets us speak freely in Chinese and express our own opinions.
老师 说 这些 作业 虽然 不 多， 但是 很 重要， 必须 做完。Lǎoshī shuō zhèxiē zuòyè suīrán bù duō, dànshì hěn zhòngyào, bìxū zuòwán.
The teacher said that although there isn’t much homework, it’s very important and must be finished.
在 学校 里， 老师 也 很 关心 学生 的 选择。Zài xuéxiào lǐ, lǎoshī yě hěn guānxīn xuéshēng de xuǎnzé.
At school, the teacher also cares a lot about the students’ choices.
老师 让 我们 回家 读 一些 文章， 然后 在 课上 自由 讨论。lǎoshī ràng wǒmen huíjiā dú yìxiē wénzhāng, ránhòu zài kèshàng zìyóu tǎolùn.
The teacher asked us to go home and read some articles, then freely discuss them in class.
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We have an entire course teaching Chinese grammar and vocabulary.