英语语法分析

What is the custom and usage in this emergence?

这里出现的习俗和用法是什么？

We saw the emergence of flight search engines such as Kayak and Skyscanner.

我们看到了诸如 Kayak 和 Skyscanner 这些航班搜索引擎的出现。

It is difficult to isolate the factors that led to the next development—the emergence of urban settlements.

推动其进一步发展，即城市聚居点出现的诸多因素，是很难孤立出来看待的。