9. Technically a given category of insurance policy is underpriced if, over time, claims against it plus expenses associated with it exceed total income from premiums. But premium income can be invested and will then yield returns of its own. Therefore, an underpriced policy does not represent a net loss in every case.

The argument above is based on which of the following assumptions?

(A) No insurance policies are deliberately underpriced in order to attract customers to the insurance company offering such policies.

(B) A policy that represents a net loss to the insurance company is not an underpriced policy in every case.

(C) There are policies for which the level of claims per year can be predicted with great accuracy before premiums are set.

(D) The income earned by investing premium income is the most important determinant of an insurance company’s profits.（E）

(E) The claims against at least some underpriced policies do not require paying out all of the premium income from those policies as soon as it is earned.

不知道为什么我会对d有疑问，刚开始就是选他，后来看了答案，知道答案是对的，但就是这个d我始终说服不了自己

(D) The income earned by investing premium income is the most important determinant of an insurance company’s profits.

我的理解是：画线部分指的应该是文中的yields

结论是 ，因为 Claim + Expense< Premium + Yield ，所以an underpriced policy does not represent a net loss in every case.

underpriced policy 本身就是Claim + Expense>remium,所以如果yield 不足够大的话（不能超过Claim + Expense） ，那么就肯定有净损失，也就是说yeilds 是一个对公司的利润有决定性的因素。

只是数学公式，不牵涉是不是最重要的收入来源问题。即使不是最重要的，也可以不赔本嘛。只要e成立就行了。