express[表达]

　　- eg: I am writing to express my gratitude for ... ;

　　covey[表达/传达]

　　- eg: i'd like to convey in this letter my appreciation for ... ;

　　sincerely[真诚地]

　　- eg: I sincerely hope that ... ;

　　extend[延伸/扩大]

　　- eg: extend my thanks for ...