Do you know about mutations? 你知道突变吗？

　　A mutation happens when the DNA structure in a gene changes. 当基因的DNA结构发生变化时就会发生突变。

　　Once a mutation happens, the change can't be reversed. 突变一旦发生，改变就无法逆转。

　　Is this difficult for you to understand? 你很难理解是吗？

　　Imagine that there is a machine, the machine gives orders to other machines. 想象有一台机器向其他机器发指令。

　　According to the orders, other machines make a car. 根据指令，其他机器制造一辆汽车。

　　If the orders change, they will make a different type of car. 如果指令变了，它们会造出一辆不同类型的汽车。

　　A mutation is like an incorrect order. 突变就像错误的指令，

　　Many people and animals are born with diseases or physical difficulties because of mutations. 许多人和动物因为突变，出生时就有疾病或生理缺陷。

　　Are mutations always bad? 突变都不好吗？

　　No, evolution is kind of mutation. 不是，进化也是一种突变。