Do you know what is inside the Earth? 你知道地球内部有什么吗?

　　There is a mantle and a core. 它里面有地幔和地核。

　　The mantle covers the core. 地幔包裹着地核。

　　Then, what is the core? 那么，什么是地核呢?

　　The core of the Earth is made of uranium. 地核是由铀组成的。

　　Imagine what a boiled egg looks like. 想象一下煮熟的鸡蛋的样子。

　　Inside the shell of the egg, there is a white part and a yellow part. 蛋壳里面有蛋白和蛋黄。

　　The white part covers the yellow part. 蛋白包裹着蛋黄。

　　If the mantle is like the white part, the core of the Earth is like the yellow part. 如果把地幔比作蛋白，那么地核就像蛋黄。

　　How about other planets? 其它行星是怎么样的呢？

　　They also have cores. 它们也有内核。