TT-2-17 为啥选E?

Tanco, a leather manufacturer, uses large quantities of common salt to preserve animal hides.  New environmental regulations have significantly increased the cost of disposing of salt water that results from this use, and, in consequence, Tanco is considering a plan to use potassium chloride in place of common salt.  Research has shown that Tanco could reprocess the by-product of potassium chloride use to yield a crop fertilizer, leaving a relatively small volume of waste for disposal.

In determining the impact on company profits of using potassium chloride in place of common salt, it would be important for Tanco to research all of the following EXCEPT:

A. What difference, if any, is there between the cost of the common salt needed to preserve a given quantity of animal hides and the cost of the potassium chloride needed to preserve the same quantity of hides?
B. To what extent is the equipment involved in preserving animal hides using common salt suitable for preserving animal hides using potassium chloride?
C. What environmental regulations, if any, constrain the disposal of the waste generated in reprocessing the by-product of potassium chloride?
D. How closely does leather that results when common salt is used to preserve hides resemble that which results when potassium chloride is used?
E. Are the chemical properties that make potassium chloride an effective means for preserving animal hides the same as those that make common salt an effective means for doing so?

我选的是C(文中已经提到了尽量减少potassium chloride 的副产品的量，那和哪个具体法规限制又有什么关系？)，但原来WORD文档中的答案是E，我觉得E和D没有什么大的区别（都是关于potassium chloride和common salt 在保护动物皮革质量和效率方面的比较）。到底答案应该是什么？请NN们指点，谢谢！