题干中出现example, case, demonstrate, illustrate等词的时候可判定为局部主题题（即例证题）。
In 1784, five years before he became president of the United States, George Washington, 52, was nearly toothless. So he hired a dentist to transplant nine teeth into his jaw-having extracted them from the mouths of his slaves.
That's a far different image from the cherry-tree-chopping George most people remember from their history books. But recently, many historians have begun to focus on the roles slavery played in the lives of the founding generation. They have been spurred in part by DNA evidence made available in 1998, which almost certainly proved Thomas Jefferson had fathered at least one child with his slave Sally Hemings. And only over the past 30 years have scholars examined history from the bottom up. Works of several historians reveal the moral compromises made by the nation's early leaders and the fragile nature of the country's infancy. More significantly, they argue that many of the Founding Fathers knew slavery was wrong-and yet most did little to fight it.
George Washington's dental surgery is mentioned to .
[A]show the primitive medical practice in the past.
[B]demonstrate the cruelty of slavery in his days.
[C]stress the role of slaves in the U.S. history.
[D]reveal some unknown aspect of his life.
题干定位：根据George Washington's dental surgery定位到第一段。
选项分析：[D]第一段说了一个不被大多数人所知道的事实，正是呼应第二段开头的这个观点，故为正解。[C]是根据第二段第二句所设置的干扰选项。排除它有两个方法：（1）选项中出现的是role of slaves，而原文中出现的是roles slavery played，已经偷换概念了。（2）but之后的观点就该和之前的观点不同了，例子也应该是为but前的观点服务的，而不是为but后的观点服务的。[B]自我总结的主观臆断选项，不否认这里能看出很残忍，但是这个例子不是为说明残忍而写的。[A]也同样，为自我总结的主观臆断选项。