发一封感谢信是必须的。

Sending a thank-you note is a must.

youdao

聚会后一星期之内向主人发一封感谢信。

Send a "thank you" note to the host within a week.

youdao

聚会后一星期之内向主人发一封感谢信。

Send a "thank you" note to the host within a week.

youdao