练习：
TN7-Q40:
Agricultural societies cannot exist without staple crops. Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods. All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams. Therefore, discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there.
Which of the following is an assumption on which the argument depends?
A. People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.
B. There are no plants native to western Africa that, if domesticated, could serve as staple food crops.
C. Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.
D. Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.
E. Kola and okra were domesticated in western Africa before rice and yams were introduced there.
TN16-Q38:
Because it was long thought that few people would watch lengthy televised political messages, most televised political advertisements, like commercial advertisements, took the form of short messages. Last year, however, one candidate produced a half-hour-long advertisement. During the half hour the advertisement was aired, a substantial portion of the viewing public tuned into the advertisement. Clearly, then, many more people are interested in watching lengthy televised political messages than was previously thought.
Which of the following is an assumption on which the argument depends?
A. The candidate’s ratings improved significantly as a result of the half-hour-long political advertisement.
B. Political advertisements have become increasingly influential in determining voters’ decisions at the polls.
C. Many people would appreciate the opportunity to become better acquainted with political candidates’ views on current political issues.
D. Most people who are interested in political issues watch television regularly.
E. Most of the viewers who tuned in to the candidate’s half-hour-long advertisement last year did not change channels after the first few minutes.
