Understanding the argument -
In these ten years - Beverage containers (BCs) accounted for a lower %age weight of household garbage. This means, say earlier, out of every 100 units of household garbage, we had 50 units of BCs, but in these years, for every 100 units, we only got ten units of BCs.
Why this happened - credit to recycling. Between the two kinds of BCs, the Aluminium (A) was recycled more than Glass Bottle (G). So what will you expect? In those ten units of garbage, we got, we would expect, say, more units of bottles and fewer units of Aluminium. Right? But the opposite of this has happened, and that is the paradox.
Just think in what scenario that'll happen. Maybe earlier, we made 20 units of Aluminum and 20 units of Glass bottles overall. Say now all manufacturers start using more Aluminium. Say now we make 38 units of Aluminium and two units of Glass. This is one possibility. Another possibility is that we use a different material altogether. Out of these 20 Aluminium cans, five are made of plastic, and the remaining 15 are aluminum, but for Glass bottles, out of 20, we now make 19 units out of plastic and 1 unit with glass. (So that you don't panic - think of 1 unit to be, for example, 1 million kilograms). Ultimately, we are trying to reduce the supply of glass bottles. This is what option C does.
Option Elimination -
(A) Glass bottles are significantly heavier than aluminum cans of comparable size. - When we compare %age - heaviness or lightness doesn't matter. Distortion.
(B) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages. The findings don't even talk about BCs or non-BCs. It just talks about Aluminium or Glass, whatever the contents may be. This is a classic distortion.
(C) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers. - ok
(D) The total weight of glass bottles purchased by households increased at a slightly faster rate than the total weight of aluminum cans. - This worsens the paradox. Opposite of what we are looking for.
(E) In many areas, glass bottles had to be sorted by color of the glass before being recycled, whereas the aluminum cans required no sorting. - Sorting doesn't help resolve the paradox. Nowhere does it say that if sorting is more difficult, it means less of that content in the garbage. At best, this may worsen the paradox.