催款信的写作步骤与语气 — 国际贸易填空题
题目
某外贸业务员甲正在撰写一封催款信（collection letter），已写出三个片段：①“We appreciate the pleasant cooperation between our two firms over the past three years...”②“However, we should like to remind you that Invoice No.105 for USD 8,600 has been overdue for 30 days...”③结尾段措辞。按催款信的标准写作步骤与语气要求，片段①属于写作步骤中的第____步；片段③的语气应保持____，避免使用指责或威胁性措辞。