The answer is B. Try negate B and see if the main conclusion still hold.
-- by 会员 sdcar2010 (2011/6/30 19:34:32)
Necessary assumption. Use negation.
If you negate B, you have "The scheduled highway projects identified as wasteful in the report WERE MOSTLY projects in districts controlled by the President’s party." If this is true, then less than 50% of the projects that are possible candidates for cancellation are in districts controlled by the rival. However, when the dust settles, 90 percent of the projects EVENTUALLY canceled were in legislative districts controlled by opposition party. Clearly we have a problem - politics is involved in the cancellation, and the main conclusion, which says otherwise, falls apart.
-- by 会员 sdcar2010 (2011/6/30 21:09:45)
A. Canceling highway projects was not the only way for the President to punish legislative districts controlled by opposition parties. - 削弱了结论
B. The scheduled highway projects identified as wasteful in the report were not mostly projects in districts controlled by the President's party. - 正确 - 如果总统掌握的10%项目被审计为垃圾，而总统并没有取消，那么就证明总统取消90%反对党项目是出于政治目地。这里恰好相反，假设10%的总统项目并非垃圾。从而支持了结论。
C. The number of projects canceled was a significant proportion of all the highway projects that were to be undertaken by the government in the near future.- 题干没说未来项目 - 不相关
D. The highway projects canceled in districts controlled by the President's party were not generally more expensive than the projects canceled in districts controlled by opposition parties. - 不相关 (题干没讨论费用问题)
E. Reports by nonpartisan auditors are not generally regarded by the opposition parties as a source of objective assessments of government projects - 政府官员的解释是依据审计报告，而审计报告作为一种客观有效的证据是必须被公认的才能作为其结论的依据。因而，如果反对党不信任审计报告，那么结论是无法被确证的，所以，本答案是削弱了结论。
-- by 会员 xfi883 (2011/7/1 9:40:35)
