你的句子用不用 one 意思不同。比较：

the person in the room 房间里的这个人

the one person in the room 房间里唯一的一个人

句意：The one person in the room who didn't hear the symphony—and never would—was the very man who composed it.

剧院里唯一没有听到并且永远也不会听到这部交响乐的那个人竟然是它的创作者。

这样用的 the one 在意义上相当于 the only。又如：

That’s the one thing ( = the only thing) I’m afraid of. 那是我唯一担心的事。

She’s the one person (=the only person) I trust. 她是我唯一信任的人。

Frank is the one man who can do it. 弗兰克是唯一能办此事的人。

The one disappointment we had was that we didn’ t get to shake hands with the President. 我们唯一失望的是没能跟总统握手。

The one disadvantage of the new software is that it uses up a lot more space on your disk. 这种新软件的唯一不好之处是，它占用的磁盘空间太大了。

She found herself in the one spot that gave her no shelter from the rain. 她发现自己处在唯一一处不能避雨的地方。