Which closing formula is appropriate for a formal business letter? A. Yours faithfully B. Best regards C. Yours sincerely D. Respectfully submitted 答案解析 核心考点：写作格式规范 解题思路：正式信函标准结尾 选项分析：C正确，A用于未知收件人，B半正式，D特定用于提交文件 易错点：可能混淆英式与美式用法差异 正确答案：C