I wrote a letter of thanks to my teacher.

我写了一封感谢信给我的老师。

He received a letter of thanks from a client.

他收到了一封来自客户的感谢信。

He wrote a letter of thanks to his teacher.

他写了一封感谢信给他的老师。

She decided to write a letter of thanks to the hospital.

她决定给医院写一封感谢信。

A letter of thanks was drawn up.

感谢信写好了.

It's courteous of you to write a letter of thanks to me.

你实在是太客气了，还写了一封感谢信给我。