core-shell

例句：

1. 1. The core of the earth is made up of rock and minerals.
   地球的核心由岩石和矿物组成。
2. 2. The outer layer of the skin is called the epidermis.
   皮肤的外层被称为表皮。
3. 3.The inner core of the planet is composed of molten metal.
   行星的内部核心由熔融金属组成。