465. I am writing to extend my sincere gratitude for...
謹以此信表達我對...的真誠感謝。

六級詞匯講解:
本句型是典型的感謝信的開頭。其中，sincere意為“真誠的；誠摯的”。如：
Please give my sincere regards to all the members of your family.
請向您全家轉達我真摯的問候。

gratitude意為“感謝的心情”。如：
We owe you a debt of gratitude for your help.
承蒙幫助，感激不盡。

本句型中，介詞for后面應該接名詞或者名詞性短語。如：your recommendations（您的推薦）、your attendance in the conference Monday（您出席周一的會議）等。

句型拓展:
I am writing to express my thanks for your presence on my birthday party.
謹以此信表達我對您參加我生日聚會的感謝。
I am writing to show my sincere appreciation for your presence on my birthday party.
謹以此信表達我對您參加我生日聚會的真誠感謝。
I feel deeply indebted to you and I really don't know how to thank you enough for your help.
我感覺欠您的太多，真不知道怎樣才能感謝您給予的幫助。