一道纠结的旧PREP逻辑，会的请不吝赐教啊~~~

桃子教主

50.    (33327-!-item-!-188;#058&007566)

When people evade income taxes by not declaring taxable income, a vicious cycle results.  Tax evasion forces lawmakers to raise income tax rates, which causes the tax burden on nonevading taxpayers to become heavier.  This, in turn, encourages even more taxpayers to evade income taxes by hiding taxable income.

The vicious cycle described above could not result unless which of the following were true?

(A) An increase in tax rates tends to function as an incentive for taxpayers to try to increase their pretax incomes.
(B) Some methods for detecting tax evaders, and thus recovering some tax revenue lost through evasion, bring in more than they cost, but their success rate varies from year to year.
(C) When lawmakers establish income tax rates in order to generate a certain level of revenue, they do not allow adequately for revenue that will be lost through evasion.
(D) No one who routinely hides some taxable income can be induced by a lowering of tax rates to stop hiding such income unless fines for evaders are raised at the same time.
(E) Taxpayers do not differ from each other with respect to the rate of taxation that will cause them to evade taxes.
正确答案为C
题目抽象成一句话就是，提高税率使得更多的人逃税。C项不是太懂，个人感觉此选项也比较绕，纠结。。。
有谁会的请不吝赐教，多谢啦~~~

月落乌啼

我觉得题目抽象出来应该是“逃税使得税率提高，税率提高又刺激更多人逃税”，单纯看这句话就觉得，前半句好像比较需要补充一个成立的条件（因为后半句基本已经很有逻辑了）。

而C选项刚好就是前半句成立的条件：收税是为了财政收入，这差不多是一个定值，那么既然有人逃税，就只能以提高税率来保证总数不变了。

小苹果

我也不懂C为什么是对的"they do not allow adequately for revenue that will be lost through evasion."
取非的话 是不是就是说如果他们允许（接受）逃税带来的损失 就不会提高税率 这个恶行循环就不会发生 结论就不成立 所以C是前提假设？

桃子教主

我觉得这不是补充一个充分条件，是补充一个必要条件。
A…not…,unless.B…这其中的逻辑关系是A推出B
也就是说恶性循环的出现导致了C：当立法者为了达到某一水平的税收而设立税率时，未能充分考虑到逃税可能带来的税收损失。
今天又想了想，不过怎么感觉越来越绕了。。。

ellie78

这是OG11th的一道题，建议楼主看看官方解释，书上解释的还蛮投的

桃子教主

啊，谢谢谢谢~~~
我用的是12版的OG，看来得抽空做11版了~~

rainbowmanutd

http://forum.chasedream.com/GMAT_CR/thread-392739-1-1.html?SearchText=prep2%2050