unknown number

例句：

1. 1. The unknown number of people who attended the event was staggering.
   参加该活动的人数令人震惊。
2. 2. The police are investigating the unidentified number of robberies that occurred last night.
   警方正在调查昨晚发生的未识别数量的抢劫案。
3. 3. The unaccounted for number of items in the warehouse has been causing concern among employees.
   仓库中未记录数量的物品已经让员工们感到担忧。