Henry III didn't know much about biology. He went through six wives back in the 1500s, looking for one whocould bear him a son. Scientists now know that it's the father's sperm, not the mother's egg, which determines whether a baby is a boy or a girl. And last week researchers at the Genetics and IVF Institute, a private fertility(生育能力)center in Virginia, announced a new technique that will allow parents to choose the sex of their baby-to-be, before it has even been conceived. The scientist used a tiny laser detector to measure the DNA in millions of sperm cells as they pass single file through a narrow tube, like cattle being herded through a corral(牲口栏). In a study published last week, "girl sperm," which has more DNA—the genetic material— in each cell, was collected, while "boy sperm" was discarded. And when purified girl sperm was used to impregnate(使受孕)a group of mothers, 15 of 17 resulting babies turned out to be girls.

The researchers say that "sex selection" can also double a mother's chance of having a son and can be usedto avoid genetic diseases that affect only one gender, such as hemophilia(血友病). But some experts, like New York University fertility specialist Dr. Jamie Grifo, worry that sex selection could lead to a kind ofin uteri(子宫)discrimination, especially in cultures where sons are considered superior to daughters. "It's valuing one gender' over another," Grifo says. "I don't think that's something we should be doing." So far, patients at the institute have been asking for both boys and girls, in order to "balance" their families. And some ethics experts say that's fine, as long as parents are just looking for a little gender variety. "If you have three boys, and you want a girl," says University of Texas reproductive-law professor John Robertson, "that's not gender bias at all."

练习题：

Choose correct answers to the question:

1.The DNA in the sperm cells can be measured ______.

A.in the same way how the cattle are herded

B.when they pass through a tube one behind the other

C.after they pass through a laser tube

D.when they are scanned by a laser detector all at a time

2.The gender of the baby is decided by ______.

A.the father's DNA

B.the mother's DNA

C.the father's sperm

D.the mother's egg四级考试试题

3.According to this passage, the practice of "sex selection" ______.

A.can help to prevent all genetic problems

B.is totally unacceptable to ethics experts

C.was already realized five hundred years ago

D.will benefit families with certain inheritable diseases

4.Girl sperm was preferred to boy sperm in the research most probably because____

A.girl sperm contains more genetic material

B.more mother want to have girl babies

C.girl sperm is healthier and more active

D.girl sperm is more easily purified

5.It can be concluded from the passage that author’s toward”sex selection”is____

A.negative

B.positive

C.neutral

D.favorable

1.[B] 推理判断题。解答本题的关键在于推断single file的意思。该句把精子通过试管的情形与牛群被赶入牲口圈的情形作对比，结合single一词本身的意思，可以推断single file是“一个接一个”的意思，只有选项B能表达这个意思，由此也可否定选项D。选项A最具干扰性，原句是把精子通过试管的情形比作牛群被赶人牲口圈的情形，而选项A说的是测定精子内DNA的方法与放牧的方法相同，显然选项A只是引用了原文的某些词语，但表达的意思与原文却截然不同。

2.[C] 事实细节题。第1段第3句which引导的非限制性定语从句修饰的是the father's sperm，而不是插入语the mother’s egg,因此选项C正确。

3.[D] 推理判断题。第2段第1句中的genetic暗示有些疾病是遗传的，即如选项D所述。第2段第1句同时表明选项A的说法是不全面的。选项B与第2段最后两句正好相反。第1段前两句说明选项C是错误的。

4.[A] 事实细节题。第1段倒数第2句中的由which引导的定语从句表明选项A的叙述正确。

5.[C] 观点态度题。文章第2段中作者给出了一些反对者和赞成者的观点，但是没有加以评论，可以看出作者的态度是中立的，故选项C正确。