During the construction, workers were told to keep out of the marked zones.

keep 在这里是动词，意思是"保持、维持"某种状态。 out 是副词，表示"在外、离开"的状态。 keep out 是一个常用短语动词，意思是"不进入、远离"，通常用于警告或禁止进入某个区域。