From 1978 to 1988, beverage containers accounted for asteadily decreasing percentage of the total weight of household garbage in theUnited States. The increasinglywidespread practice of recycling aluminum and glass was responsible for most ofthis decline. However, although aluminumrecycling was more widely practiced in this period than glass recycling, it wasfound that the weight of glass bottles in household garbage declined by a greaterpercentage than the weight of aluminum cans.
Which of the following, if true of the United States inthe period 1978 to 1988, most helps to account for the finding?
(A) Glass bottles are significantly heavier than aluminumcans of comparable size.
(B) Recycled aluminum cans were almost all beveragecontainers, but a significant fraction of the recycled glass bottles hadcontained products other thanbeverages.
(C) Manufacturersreplaced many glass bottles, but few aluminum cans, with plastic containers.
(D) The total weight of glass bottles purchased byhouseholds increased at a slightly faster rate than the total weight ofaluminum cans.
(E) In many areas, glass bottles had to be sorted bycolor of the glass before being recycled, whereas aluminum cans required nosorting.
参考答案: C
思路：需要解释的现象：the weight of glass bottlesin household garbage declined by a greater percentage than the weight ofaluminum cans..
正确答案作用：1. 需要解释这个比较，所以答案也是要比较glass bottles 和aluminum cans;2. 最好用转折前的现象来解释转折后的现象。
思考：aluminum cans 被recycle的数量很多，为什么下降的比例没有那么多。很明显，这是一个比例和绝对数量的问题。那就是aluminum cans在市场中的基数比glass bottles多。
选项分析：A：虽然是glass bottles跟aluminum cans的比较，但是哪个更重跟需要解释的现象没有关系;
B：也是在对比glass bottles和aluminum cans。 但是对比的是它们是不是beverage containers, 这个跟谁的基数大没有关系。并且有范围扩大词other than;
D：glassbottles购买的增加比aluminum cans多，文章中又说recycle的 aluminum cans 比较多，那应该说明aluminum cans下降的比较多才对，与现象刚好相反，也和我们的“思考的市场中的基数”刚好相反;
E: 在被recycle之前，到底会不会根据颜色分类，与它们比例的下降没有关系;
C：确实是对比glass bottles和aluminum cans。制造商用plastic containers替换了很多的glass bottles而几乎没替换aluminum cans。这说明在市场中，glass bottles较少，aluminum cans较多，也就是aluminum cans基数大。刚好解释了为什么aluminum cans的下降比例少。正确答案。