key pulley

例句：

1. 1. The key to solving this problem lies in understanding the underlying mechanics of the system.
   解决这一问题的关键在于理解系统背后的工作原理。
2. 2. The pivot point of the project is to improve efficiency and reduce costs.
   该项目的关键点在于提高效率和降低成本。
3. 3. The keystone of the ecosystem is the balance between predators and prey.
   生态系统的关键要素是捕食者和猎物之间的平衡。