Question 13 is based on the passage you have just heard.

         (12) [Public interest was aroused by the latest discovery of a changed gene in obese mice. ]The news was made known by Rockefeller University geneticist Jeffrey Friedman. The researchers believe this gene influences development of a hormone that tells organism how fat or full it is. (13) [Those with the changed gene may not sense when they have eaten enough or if they have sufficient fatty tissue, and thus can’t tell when to stop eating. ]

        The researchers also reported finding a gene nearly identical to the mouse obesity gene in humans. The operation of this gene in humans has not yet been demonstrated, however. (14) [Still, professionals like University of Vermont psychologist Esther Rothblum reacted enthusiastically, “This research indicates that people really are born with a tendency to have a certain weight, just as they are to have a particular skin color or height.” ]

        Actually, behavioral geneticists believe that less than half of the total weight variation is programmed in the genes, while height is almost entirely genetically determined. Whatever role genes play, Americans are getting fatter. A survey by the Center for Disease Control found that obesity has increased greatly over the last 10 years. (15)[ Such rapid change underlines the role of environmental factors like the abundance of rich foods in Americans’ overeating. ]The Center for Disease Control has also found that teens are far less physically active than they were even a decade ago.

        Accepting that weight is predetermined can relieve guilt for overweight people. But people’s belief that they cannot control their weight can itself contribute to obesity.

13. What do we learn about the changed gene?（关于变异基因我们可以知道什么？）

解析：D。根据四个选项中的renders、prevents和helps，推测题干可能会问某事物产生的作用或影响。录音中说到具有变异基因的老鼠（Those with the changed gene）不知道什么时候该停止进食。D项中的unable to sense对应录音中的can’t tell，when to stop eating属于原词复现，故D项正确。

错项排除：A项和C项利用录音中出现的Disease和environmental进行干扰，但选项内容与录音中所表达的相差甚远，故均可排除。录音中提到fatty tissue，但只是说老鼠不知道自己是否已经储存了足够的脂肪组织，并没有说变异基因是否会影响脂肪组织的形成，故B项错误。