间谍在人群中移动，未被察觉。

The spy moved through the crowd ___unnoticed.

许多社会变化在变得不可否认之前一直未被注意到。

Many societal changes occur ___unnoticed until they become undeniable.

在忙碌的工作场所中，她的贡献经常被忽视。

Her contributions often go ___unnoticed in the busy workplace.