[求助]急！ prep 23求助。。。

From 1978 to 1988, beverage containers accounted for a steadily decreasing percentage of the total weight of household garbage in the United States.  The increasingly widespread practice of recycling aluminum and glass was responsible for most of this decline.  However, although aluminum recycling was more widely practiced in this period than glass recycling, it was found that the weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.

Which of the following, if true of the United States in the period 1978 to 1988, most helps to account for the finding?

(A) Glass bottles are significantly heavier than aluminum cans of comparable size.

(B) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages.

(C) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.

(D) The total weight of glass bottles purchased by households increased at a slightly faster rate than the total weight of aluminum cans.

(E) In many areas, glass bottles had to be sorted by color of the glass before being recycled, whereas aluminum cans required no sorting.

答案是C。。我不太明白什么意思

题目是说，垃圾总的重量减少的原因是因为以前垃圾中的饮料瓶被用来回收了。

回收的饮料瓶中，铝制的瓶子比玻璃瓶更常用，所以铝制的瓶子重量的减少对垃圾总量的减少的贡献应该大于玻璃瓶

但是实际上， 玻璃瓶在总垃圾中减少的重量比铝制品大很多？问为什么

C选项是说制造商都用塑料瓶来替换玻璃瓶了

非常不解的地方在于，就算是制造商把绝大部分的玻璃瓶替换成塑料瓶了，那对推理过程也没帮助

比如，原来垃圾有100斤，其中有15斤的玻璃瓶和5斤的铝瓶。

那么回收之后，总垃圾变成80斤了，因为15斤的玻璃瓶和5斤的铝瓶被回收了，

其中玻璃瓶对垃圾减少的贡献为15斤，铝瓶为5斤

如果像C选项所说，其中有10斤的玻璃瓶被替换成塑料瓶了

那其中玻璃瓶对垃圾减少的贡献还为15斤，铝瓶还为5斤，因为垃圾中以前有15斤的玻璃瓶，现在都没了！

所以C选项似乎对整个推理过程没有任何帮助啊！

扔掉的饮料罐的重量越来越少。原因：AG的回收。

但是，虽然A的回收率大于G，G减少的却A比多。

极端假设：G用完都扔了，完全不被回收。

那G还减少量还比A多，说明G使用的就少。
            

谢谢LS两位的解释：）

原来自己的理解有误。。认为所有的玻璃瓶和铝瓶都已经被回收了。。。