Do you know what an egg cell is? 你知道什么是卵细胞吗？

　　An egg cell is necessary for reproduction. 卵细胞是繁殖的必要条件。

　　Animals have egg cells. 动物有卵细胞。

　　Then does every animal have egg cells? 那么每个动物都有卵细胞吗?

　　No, they don't, only female animals have egg cells. 不是的，只有雌性动物有卵细胞。

　　Male animals have sperm cells instead. 雄性动物有精子细胞。

　　When an egg cell meets a sperm cell, they work together and creat a new animal. 一个卵细胞遇到精子细胞后，它们共同努力创造出新生命。

　　Can an egg cell alone create a new animal? 一个单独的卵细胞能创造出一个新的动物吗？

　　No, it always needs a sperm cell. 不能，要有精子细胞才可以。

　　Usually,one egg cell and one sperm cell become one animal. 通常情况下，一个卵细胞和一个精子细胞会创造出一只动物。

　　However, sometimes they split into two, and become two anminals, we call these animals twins. 但有时，它们会分裂成两个细胞，创造出两只动物，我们称它们为双胞胎。