请教OG104

104. Spending on research and development by United States businesses for 1984 showed an increase of about
8 percent over the 1983 level. This increase actually continued a downward trend evident since 1981 – when
outlays for research and development increased 16.4 percent over 1980 spending. Clearly, the 25 percent tax
credit enacted by Congress in 1981, which was intended to promote spending on research and development,
did little or nothing to stimulate such spending.
The conclusion of the argument above cannot be true unless which of the following is true?
(A) Business spending on research and development is usually directly proportional to business profits.
(B) Business spending for research and development in 1985 could not increase by more than 8.3%
(C) Had the 1981 tax credit been set higher than 25%, business spending for research and development after 1981 would have increased more than it did.
(D) In the absence of the 25% tax credit, business spending for research and development after 1981 would not have been substantially lower than it was.
(E) Tax credits market for specific investments are rarely effective in inducing businesses to make those investments.

答案是D。以下是我推理过程，虽然推出来了，但我自己感觉疙疙瘩瘩的，不顺畅。请NN帮我看看其中有没有错的地方，谢谢！

题干：花在R&D上的钱的增长率由逐年下降的趋势，显然tax的政策没能促进花费。

问：只有下面哪个对了，才能支持原文结论。

D：如果没有这个tax政策，1981年以后的花费就不会比现在更低，即花费会比现在高。现在有这个政策却低了，所以这个政策没用。

assumption

结论：tax credit没有起作用

前提：排除其他原因导致的花费减少

D：如果没有tax credit，花费会多。排除了有其他可能导致花费减少的情况。

再问一下：为什么B不对？

B取非：1985年R&D花费的增加将大于8.3%，所以tax还是起到作用了。所以，削弱结论。

请问我上面的推理哪里不对？难道：如果1985年的花费增加只有8.4%，就只是一点点作用，或者说几乎没有，支持了结论？这个解释肯定太牵强，请NN帮忙指正，谢谢！

对于B这个项目，我觉得楼上不应该去把8.3和16.4去比，他和8的效果都是一样的。

而且我感觉Assumption和Conclusion题目的答案一定要是原文推理的内涵，而不能是外延（Infer才是外延）。1985年怎么样都是推测，已经超出了原文推理的范围，应该不会作为Assumption题目的答案的。

可以看看http://forum.chasedream.com/dispbbs.asp?boardID=24&ID=50691&page=2。

不过只是个人感觉，如果说得不对，还请多多指教：）