在英文学习的过程中，“which”引导的定语从句属于比较重要的语法点，按照以前学习的语法知识，“which”引导定语从句的主要用法如下面例句所示：

1. The acquisition of any share of stock or any security which results in the nondeductibility of a loss under the provisions of this section shall be disregarded in determining the deductibility of any other loss.

（在确定任何其他损失的可抵扣程度时，购入任何导致本条项下损失不可抵扣的股票或证券应忽略不计。）

2. While no liability shall be taken into account before economic performance and all of the events that fix the liability have occurred, the fact that the exact amount of the liability cannot be determined does not prevent a taxpayer from taking into account that portion of the amount of the liability which can be computed with reasonable accuracy within the taxable year. For example, A renders services to B during the taxable year for which A charges $10,000. B admits a liability to A for $6,000 but contests the remainder. B may take into account only $6,000 as an expense for the taxable year in which the services were rendered.

（虽然在产生经济效益并且确定责任的全部事件发生之前不应考虑任何责任，但是，无法确定确切的责任金额并不会妨碍纳税人计入能够在纳税年度合理准确计算的责任金额。比如，A在纳税年度向B提供了服务，A向B收取10,000美元，但是B认为应收取6,000美元，对其余收费存有异议，那么，B只能将6,000美元计作服务提供所在纳税年度的费用。）

上述两个例子中，“which”引导的从句都是常见且属于比较简单的定语从句，但是，接触过法律英语后发现，“which”还有更高级的用法。众所周知，法律条文一般都比较长，甚至一个段落只有一句话，这个时候“which”发挥了重要作用，例句如下所示：

Where more than one loss is claimed to have been sustained within the taxable year from the sale or other disposition of stock or securities, the provisions of this section shall be applied to the losses in the order in which the stock or securities the disposition of which resulted in the respective losses were disposed of (beginning with the earliest disposition). If the order of disposition of stock or securities disposed of at a loss on the same day cannot be determined, the stock or securities will be considered to have been disposed of in the order in which they were originally acquired (beginning with the earliest acquisition).

这段话中，使用了三个“which”，其中，第一个和第三个“which”属于同一种用法，也是常用的简单用法，比较特殊的是“the stock or securities the disposition of which”，这种用法平常几乎没见过，但是在法律英文中却会常见。在“in the order in which the stock or securities the disposition of which resulted in the respective losses were disposed of”这句话中，存在两个定语从句，第一个就是“in the order in which...”，这个从句中的主语是“the stock or securities”，谓语是“were disposed of”；第二个则是“the stock or securities the disposition of which...”，这个从句中的主语是“disposal”，谓语是“resulted in”，宾语是“respective losses”，此处“of which”中的“which”指代“stock or securities”，通过这样的方式，句子结构更紧凑，更符合法律用语习惯。

译文参考如下：

如果声称在纳税年度因出售或以其他方式处置股票或证券而遭受不止一项损失，则本条规定应按照经处置导致损失的股票或证券处置顺序（从最早的处置开始）适用于损失。如果无法确定同一日亏本处置的股票或证券顺序，则股票或证券将被视为已按照最初购入的顺序（从最早的购入开始）处置。

来源：

Code of Federal Regulations