If you mom's blood type is O and your dad's blood type is A. 如果你妈妈是O型血，你爸爸是A型血。

　　Your blood type must be either A or O. 那你不是A型血就是O型血。

　　How do we know this fact? 我们是怎么知道这个事实的？

　　Because some scientists study human blood types, we know that one's blood type is determine by the blood types of one's parents. 因为有些科学家研究人类的血型，所以我们知道一个人的血型是由他的父母决定的。

　　What do we call these scientists? Geneticists. 我们怎样称呼这些科学家？遗传学家。

　　Geneticists are the scientists that study genes and heredity. 遗传学家是研究基因和遗传的科学家。

　　Geneticists usually study medicine, biology, chemistry and so on. 遗传学家通常研究医学、生物学，化学等等。

　　These days, some geneticists are working to make human clones. 如今，有些遗传学家正在从事克隆人类的工作。

　　Do you think it is possible? 你认为这行得通吗？

　　They think it is. 他们认为行得通。