该计划现在比预定的计划晚了7年，首先是因为费用增加，其次是由于技术问题。

The programme is now seven years behind schedule as a result, firstly of increased costs, then of technical problems.

《柯林斯英汉双解大词典》

首先是因为刺激计划糟糕的效果。

The first is the poor results of the stimulus plan.

youdao

首先是因为他们有这个能耐。

The first is that they can.

youdao

Well, of course, it's because he thinks, first of all, there's a soul and it will survive and it's immortal.

当然,这是因为他认为,首先,灵魂是存在的,在肉体死后仍会继续存在,而且灵魂是不朽的

耶鲁公开课 - 死亡课程节选

because, first of all, the salary is not very... high.

而首先是因为这个行业的薪水并不很......高。

建筑学专业教授 - SpeakingMax英语口语达人

Well, first it is important because it's-- you need to track what the population is eating and also individual intake.

说它重要首先是因为,你需要探寻人们都吃什么,还有个体摄入量

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选