It is the first time that we travel. 在这个定语从句中

It is the first time that +现在完成时
It was the first time that+过去完成时
一般作为一个句型来记的
要解释的话,有点难
因为他肯定是作状语
We travel for the fisrt time
说什么for the fisrt time也是状语
那为什么前面用关系代词that呢
所以只能作为一个句型来记
time作“一段时间”解 用when=at which
There was a time when the song was popular
作“次数”解,用that