I am writing

·in response to n·P.

·in regard to n.p.

我写信

回答...

考虑到...

·in connection with n.p.

·on behalf of n. p.

与...联系

代表...

I am writing to

·ask about n.P.

·confirm n.P.

·confirm that+n.clause

·cancel n.P.

·request n .P.

·clear up n.P

·enquire about n.P.

我写信

询问...

证实...

证实+名词性从句

取消...

要求...

弄清楚...

要求...

·inform you of n. p·

·inform you that+n. clause

·let you know that+n.clause

·let you know about n.P·

·tell you that+n.clause

·thank you for n. p. /Ving

通知你+名词短语

通知你+名词从句

让你知道+名词短语

让你知道+名词从句

告诉你...

感谢你...