He remembered past kindness of a friend. And wrote him a thankyou letter.

他记起一位朋友昔日的恩情，便写给他一封信表示感谢。

youdao

And wrote him a thankyou letter.

便写给他一封信表示感谢。

youdao

And wrote him a thankyou letter.

便写给他一封信表示感谢。

youdao