2．Cloning stem cells (干细胞) for research

　　Stem cells are the body's bulding blocks which might be used to repair damaged or diseased organs and tissues. Researchers are currently looking toward cloning as a way to create genetically defined human stem cells for research and medical purposes.

　　3．Reviving endangered or extinct species

　　Dinosaur was an extinct species. Could we really clone dinosaurs? In theory? Yes. What would you need to do this? A well­preserved source of DNA from the extinct dinosaur, and a closely related species, currently living, that could serve as a surrogate(代用的 ) mother. In

　　reality? Probably not. It's not likely that dinosaur DNA could survive undamaged for such a long time. However, scientists have tried to clone species that became extinct more recently, using DNA from well­preserved tissue samples.

　　4．Cloning humans

　　Why would anyone want to clone humans？Some reasons are to help infertile_couples have children or to replace a decreased child.However, there are the risks involved.For example，how sure can we be that a cloned baby will be healthy or what might go wrong?

　　【语篇解读】 为什么要研究克隆技术？它对人类有利的方面是什么？

　　1．What's the main idea of the whole passage?

　　A．Why people use cloning.

　　B．How to clone animals.

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