填空题解题技巧 — 英语词汇题

听力填空题中，若录音中说话人将题干提示词 "reserve a room" 转述为 "we've set something aside for you"，且空格所在句为：Guests must show a valid ______ when checking in. 录音原文为：Please remember to bring your passport, as other forms of identification will not be accepted at the front desk. 根据填空题同义转换与限定信息排除技巧，空格处应填入的单词是：