In April scientists in China said they had tried using CRISPR to edit the genomes (基因组) of human embryos. Though the embryos would never turn into humans, this was the first time anyone had ever tried to edit DNA from human beings. With this in mind, the US National Academy of Sciences plans to discuss questions about CRISPR's ethics (伦理问题).

　　For example, CRISPR doesn't work properly yet.As well as cutting the DNA it is looking for, it often cuts other DNA, too. In addition, we currently seem to have too little understanding of what DNA gives people what qualities.

　　There are also moral questions around "playing God". Of course, medicine already stops natural things from happening-for example, it saves people from infections. The opportunities to treat diseases make it hard to say we shouldn't keep going.

　　A harder question is whether it is ever right to edit human germ-line (种系) cells and make changes that are passed on to children. This is banned in 40 countries and restricted in many others. However, CRISPR means that if genes can be edited out, they can also be edited back in. It may be up to us as a society to decide when and where editing the genome is wrong.

　　Also, according to The Economist, gene editing may mean that parents make choices that are not obviously in the best interests of their children: "Deaf parents may prefer their children to be deaf too;parents might want to make their children more intelligent at all costs."

　　In the end, more research is still needed to see what we can and can't do with CRISPR. "It's still a huge mystery how we work," Craig Mello, a UMass Medical School biologist and Nobel Prize winner, told The Boston Globe. "We're just trying to figure out this amazingly complicated thing we call life."

1.What is the article mainly about?

　A.How CRISPR was developed by scientists.

　B.What we can and can't do with CRISPR.

　C.Chinese scientists' experiment of using CRISPR to edit human embryos.

D.The advantages of CRISPR and arguments about its ethics.