首先你必须通过移民局和海关的检查。

First, you have to go through immigration and customs.

《柯林斯英汉双解大词典》

首先你必须让发动机转起来预热。

In the first place you must rev it up to warm the engine.

youdao

首先你必须告诉我，它们是否开始工作。

First you have to tell me whether they are working.

youdao

You take all the risky assets ... and you analyze them first to get their-- you have to do a statistical analysis to get their expected returns, their variances, and their covariances.

你需要对所有的风险资产进行分析,首先要得到它们的-,你必须要做一个统计分析,算出它们的预期收益率，方差，和它们的协方差。

耶鲁公开课 - 金融市场课程节选

The challenges that... First of all, you got to understand that learning a language takes time.

挑战就是，首先，你必须明白学习一门语言是件耗时间的事。

学第二外语的时候 - SpeakingMax英语口语达人

Well, I think the first thing is like you really have to want to learn it.

嗯，我觉得首先是你真的必须想学。

学习外语的时候 - SpeakingMax英语口语达人