Write a letter thanking a teacher who helped you.

Pronouns are the whole test here. Call the teacher THẦY for a man or CÔ for a woman, and call yourself EM — even if you are an adult. The teaching relationship overrides age.

End respectful sentences with Ạ. Leaving it out makes the letter sound flat.

Standard closing: «Em xin cảm ơn thầy ạ.» or «Em chúc thầy nhiều sức khoẻ.»