当 some 所表达的意义为 a certain “某一；某个”时，可接可数名词的单数形式。牛津高阶英汉双解词典》有如下解释：

(used with sing [C] ns 与单数可数名词连用) person, place or thing that is unknown or unspecified 未知的或未确指的人﹑ 地点或事物: 

Some man at the door is asking to see you. 门口有人要见你。

She won a competition in some newspaper or other. 她参加某报纸举办的比赛获胜。

▲再提供两个词典例句：

He is working at some place in the north. 他在北方某地工作。《现代汉英综合大词典》

Some careless man has taken my umbrella.某个粗心大意的人拿走了我的雨伞。《21世纪英汉汉英双向词典》