Which of the following is the standard closing formula for formal business correspondence?

A. Yours truly,

B. Best wishes,

C. See you soon,

D. Sincerely yours,

核心考点：写作格式规范解题思路：正式商务信函标准结尾为'Sincerely yours'。其他选项适用于不同场景：A半正式，B非正式，C口语化。选项分析：D符合商务规范；A适合普通信件；B/C过于随意易错点：混淆不同场合的格式要求

正确答案：D