Dear ______ ,
①I am writing to extend my sincere gratitude for ______（感谢的原因）. ②If it had not been for your assistance in ______（对方给予的具体帮助）, I fear that I would have been ______（没有对方帮助时的后果）.
③Every one agrees that it was you who ______（给出细节）.
④Again, I would like to express my warm thanks to you! Please accept my gratitude.