core pin

例句：

1. 1.The core of the machine is made of steel.
   这台机器的核心部分是用钢制成的。
2. 2. The center of the city is bustling with activity.
   这座城市的中心地区繁忙活跃。
3. 3. The core of the problem lies in the lack of communication.
   问题的核心在于缺乏沟通。