第二遍看OG，但对这个195还是有些小问题，盼NN指教。

195. A proposed change to federal income tax laws would eliminate deductions from taxable income for donations a taxpayer has made to charitable and educational institutions. If this change were adopted, wealthy individuals would no longer be permitted such deductions. Therefore, many charitable and educational institutions would have to reduce services, and some would have to close their doors. The argument above assumes which of the following? (A) Without the incentives offered by federal income tax laws, at least some wealthy individuals would not donate as much money to charitable and educational institutions as they otherwise would have. (B) Money contributed by individuals who make their donations because of provisions in the federal tax laws provides the only source of funding for many charitable and educational institutions. (C) The primary reason for not adopting the proposed change in the federal income tax laws cited above is to protect wealthy individuals from having to pay higher taxes. (D) Wealthy individuals who donate money to charitable and educational institutions are the only individuals who donate money to such institutions. (E) Income tax laws should be changed to make donations to charitable and educational institutions the only permissible deductions from taxable income.

A，B，E如果取非都能对结论起到否定的作用。为什么单单选择了A？是因为B和E中的only太过绝对？

谢谢。

题目问得是前提条件，即是必要条件，起到对文中的前提与结论之间架桥的作用。

而B，E不是必要条件，都不是必要的。

如B说的这笔钱是不是唯一的与题目中的前提没有减免税收跟一些机构关门没有连接作用的。(从下面对A的解释可以得出，即使是唯一财源，但是它并不受到税收减免政策的影响，那么也不会到结论。)

而A架起了之间的gap，前提：新政策没有税收减免，A没有减免导致部分人不愿意捐款，结论：一些机构关门。

but D also filled the gap between "wealthy individuals" and "who donate money to such institutions".

and if it negnative, the conclusion cannot hold.

so , why? thanks very much.

D的原因跟B的差不多呀，

Wealthy individuals who donate money to charitable and educational institutions are the only individuals who donate money to such institutions.

即使他们是唯一的捐助者，那么跟文中说的减免税收没有任何关系呀！他们不受减免税收的影响的话，解释没有优惠政策，他们仍然捐助的话，那些机构也不会关门啊！