upon arriving home ,the girl discovered that she had left her bag at her friend's.这里面的upon是什么意思?
问题描述：
upon arriving home ,the girl discovered that she had left her bag at her friend's.这里面的upon是什么意思?
答
upon=on 介词
表示当...时候,相当于时间状语从句
当到家的时候,这个女孩子发现她把包落在她朋友家里了