先後

先後

"Order" or "sequence."

In this sentence, "先後" is used to describe the sequential order in which the individuals completed the project.

他們先後完成了這個項目。

They completed the project one after another.

Here, "先後" is used to emphasize the importance of the sequence or chronological order of events.

先後的次序很重要，因此要確保一切有條不紊。

The order of sequence is very important, so it's necessary to ensure everything is organized.

This usage of "先後" indicates the consecutive timeline of visiting attractions during the journey.

旅程中我們先後參觀了幾個景點。

During the journey, we visited several attractions in succession.