2. 外语
  3. Henry III didn’t know much about biology. He went through six wives back in the 1500s, looking for one who could bear him a son.

Henry III didn’t know much about biology. He went through six wives back in the 1500s, looking for one who could bear him a son.

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问题     Henry III didn’t know much about biology. He went through six wives back in the 1500s, looking for one who could 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 used to 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 of in 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."
The DNA in the sperm cells can be measured ______.
选项 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
答案B
解析 解答本题的关键在于推断single file的意思。本句把精子通过试管的情形与牛群被赶人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。
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