In this task, You are given an open-domain question that can be answered based on factual information. Your task is to provide \*short\* answer (in a few words only) for the given question. The short answer can be one or more entities or it can also be boolean \*yes\* or \*no\*.
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Question: how long is a tracking number for ups

Answer: 18 characters


Question: what type of stone did the romans use

Answer: Travertine limestone


Question: how does the oral cavity help the digestive system

Answer:
produces a lubricating mucus