iron core

例句：

1. 1. The iron core of the machine is what makes it work.
   机器的铁心是它工作的原因。
2. 2.The story's iron core is that it's not just about love but also about loss.
   这个故事的核心是，它不仅仅是关于爱情，也是关于失去。
3. 3. The company's iron core strategy has been a key driver of its success.
   公司的铁心战略一直是其成功的关键驱动力。