70. 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 non—evading 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．
这道题目的答案是C但是我不明白，题目的意思是不是因为很多人逃税，所以政府不得不加重税率，这样的话那些不逃税的人的税率就加大了，所以逃税的人就更多了，C是什么意思呢？谢谢大家。

题目说的是一个恶性循环:
逃税 -> 加税 -> 更多的人逃税.
恶性循环的Assumption是 "不存在打破恶性循环的条件"

(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．

C说的是一个打破恶性循环的条件不存在: 法律制定者在制定收入税率时没考虑到逃税的损失.