Question 15 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.

15. What accounts for Americans’ obesity according to a survey by the Center for Disease Control?（根据疾病控制中心所做的调查，是什么导致了美国人的肥胖问题？）

解析：B。录音后半部分提到了疾病控制中心认为美国肥胖人数大幅增加，凸显了环境因素的影响，比如美国人大量食用油腻食品（rich foods）。由此可知油腻食品是导致美国人肥胖问题的一大原因，B项中的abundant provision of rich foods是对录音中abundance of rich foods的同义替换，故B项正确。

错项排除：录音中虽然提到environmental factors，但在这里指“外部环境因素”，且随后举了油腻食品的例子加以解释，并不是指自然环境，故A项排除。C项中的present-day life和D项中的food industry在录音中未提及，故排除。