2. 例子与概述合二为一
有时例子与概述合二为一，它们分别出现于从句和主句中，或者出现于同一个分句中。例如，
Scholars offer three related but different opinions about the mysterious origin and significance of these paintings. One opinion is that the paintings were a record of seasonal migrations made by herds. Because some paintings were made directly over others, obliterating them, it is probable that a painting’s value ended with the migration it pictured. Unfortunately, this explanation fails to explain the hidden locations, unless the migrations were celebrated with secret ceremonies.
Why does the author mention secret ceremonies?
To present a common opinion held by many scholars
To suggest a similarity between two opinions held by scholars
To suggest a possible explanation for a weakness in an opinion expressed in the passage
To give evidence that contradicts a major opinion expressed in the passage
问题中的关键词secret ceremonies出现于段落末句的从句中：unless the migrations were celebrated with secret ceremonies。在同一句子的主句部分，作者指出：不幸的是，这一解释未能说明为何绘画的位置要隐蔽…，这等于说这一解释不能成立;接着在问题所对应的从句中补充说明上述解释成立所必须满足的条件：除非迁徙的庆祝是秘密进行的。这等于说这一解释缺乏这一条件。第三个选项符合此意，为正确答案。
3. 一段中两个相距较远的例子说明该段主题句
问题中涉及同一段中两个例子、而且它们不在一处时，通常它们说明该段主题句。例如，
Mass transportation revised the social and economic fabric of the American city in three fundamental ways. It catalyzed physical expansion, it sorted out people and land uses, and it accelerated the inherent instability of urban life. By opening vast areas of unoccupied land for residential expansion, the omnibuses, horse railways, commuter trains, and electric trolleys pulled settled regions outward two to four times more distant from city centers than they were in the pre-modern era. In 1850, for example, the borders of Boston lay scarcely two miles from the old business district; by the turn of the century the radius extended ten miles. Now those who could afford it could live far removed from the old city center and still commute there for work, shopping, and entertainment. The new accessibility of land around the periphery of almost every major city sparked an explosion of real estate development and fueled what we now know as urban sprawl. Between 1890 and 1920, for example, some 250,000 new residential lots were recorded within the borders of Chicago, most of them located in outlying areas. Over the same period, another 550,000 were plotted outside the city limits but within the metropolitan area. Anxious to take advantage of the possibilities of commuting, real estate developers added 800,000 potential building sites to the Chicago region in just thirty years – lots that could have housed five to six million people.
18. Why does the author mention both Boston and Chicago?
(A) To demonstrate positive and negative effects of growth.
(B) To show that mass transit changed many cities.
(C) To exemplify cities with and without mass transportation.
(D) To contrast their rates of growth
问题中的关键词Boston与Chicago是两个例子，它们前面分别有提示词for example。由于两个例子位于同一段，而且不在一处，因此只能说明本段主题，也就是首句：Mass transportation revised the social and economic fabric of the American city in three fundamental ways。选项(B)符合此意，为正确答案。
