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.

  不太明白 意思~~

谢谢！！！

人们通过不声明纳税收入来逃税，一个恶意循环就发生了。逃税迫使lawmaker提高税率，而更高的税率又使得更多的人通过隐藏纳税收入逃税。

问题：除非下列那个是真的，恶意循环将不会发生。其实问的是，如果恶意循环发生了，下面那个是真的。感开始也被这个not unless搞糊涂了，到底是a》b还是b》a，呵呵，

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.税率对纳税人增加他们的税前收入有刺激作用，税前和taxable有区别，而且即使没有区别他们申不申明又是一回事，因此无关。

(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.侦查逃税的方法，文中说，因此无关。

(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.当lawmakers设定想取得一定收入水平的税收的税率时，他们没有充分考虑到那些从逃税中损失的税收。这个条件很是隐讳，问题把前提已经给了（恶意循环已经发生了），提到lawmaker是在提高税率时提到的，那么恶意循环发生的时间应该是在提高税率后(而不是前面部分的偷税行为)，而是更多的人偷税的行为。这个lawmaker提高税率的想法是想弥补前面的偷税损失，而没有想到税率提高使得更多的人偷税。（但是要说的是这个选项实际上也只是相对正确的选项，也许lawmaker考虑到了更多的人偷税呢，但是他就是把那些老实巴交的人征奇高的税也能取得一定水平的收入，总有老实人吧，但这是后话了）

(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.那些偷税的人没有人会因为降低税率而不偷税，除非罚款也提高到同样的水平。罚款也没有在文中提到吧，也是无关选项。即使不看无关，这句话重写为：如果偷税的人不偷税了，那么一定是罚款也提高到了同样的水平。也许还因为罚款更高呢。

(E) Taxpayers do not differ from each other with respect to the rate of taxation that will cause them to evade taxes.纳税人在他们各自引导他们偷税的那个税率上都是互不相同的。也无关吧，这是taxpayers的心里感受吧，呵呵。

如果这个成立(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.当lawmakers设定想取得一定收入水平的税收的税率时，他们没有充分考虑到那些从逃税中损失的税收

tax rate就不变，所以恶性循环就不发生了？

Correct. The vicious circle does not happen b/c the lawmakers do not take the tax evasion into account when set the tax rates so that the tax rates will not be high enough to cause more people choose tax evasion.

注意：  the only way that/of A is B  可以推出 A→B 或 非B→非A

    A unless B  可以推出 非A → B 或 非B →A

      若A, must B 可以推出 A→B