the first statement gives a fact -"plastics constitute a smaller proportion by weight or volume than paper products".
the second sentence - "similar weight/volume leads to same amount of damage".
the first two sentences support (hence, premise) for the third sentence. the 3rd sentence acts as a conclusion -
"the current use of plastics actually does less harm to the environment nationwide than that of paper products."
Which option states this? Option E.
Note that this is also preceded by the conclusion indicator "therefore".
Let us look at the answer options -
Option A - Incorrect.
this is not the author's conclusion/opinion. It is just an evidence/fact stated.
Option B - Incorrect.
Cannot be inferred. We only know this - "The damage that a given weight or volume of trash does to the environment is roughly the same".
this does not mean that "weight/volume" (density) for both plastics and paper products is the same.
Option C - Incorrect.
"popular opinion" is not the "author's opinion/conclusion". In fact, the author's opinion is "contrary" to the popular opinion.
Option D - Incorrect.
Incorrect. Because the argument clearly states that both paper/plastics cause same amount of damage per weight or volume. Hence, shifting to paper products is unlikely to help.