I'm unclear how questioning the nature of compounds would help us here.
You are correct.
I overlooked this fact.
Major problem with B,C,and D is lack of
that.
E, however, is non-sensical because of illogical meaning communicated by present participle phrase.
Knowing only this much is more than enough to eliminate incorrect answer choices.
Following stuff is not necessary to get to the correct answer.
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Present participle phrase, when used w/o commas, modify noun;i.e, they tell us more information about noun.
That information is typically a state--a temporary state-- and is true for the time period communicated by tense of a clause.
That information can also be used to distinguish a noun( the one being modified by participle phrase) from other nouns of the same category, if that noun represents a category and not a member of that category.(general vs specific situation.)
I saw Arthur running for the bus.
running for the bus is a participle phrase.
running for the bus is a temporary state of Arthur.
Message communicated is that when i saw Arthur, he was running for the bus.
In this situation, asking
which Arthur? what kind of Arthur? doesn't make sense because there is only one Arthur: Arthur is not a category. We are being specific here.
I saw a boy running for the bus.
running for the bus is a participle phrase.
running for the bus is a temporary state of a boy.
Message communicated is that when i saw a boy, he was running for the bus.
In this situation, asking
which boy? etc. makes sense because boy is a general term.
Similarly,
Cat sleeping on the rug is named Sue.
which cat? which one? which one are we talking about?
The one sleeping on the rug and not the one ,say, sleeping on the couch.
Enter choice E-
studies showed the compounds entering into the food chain...
the is not same as a( above example)
the is specific/ definite article whereas a is indefinite article( not specific).
THE is perfectly fine to talk about something which has been previously mentioned, introduced, or discussed.
Term the compounds in all answer choices, thus, points towards PCBs.
Hence asking which compounds? or what kind? doesn't make sense.
In official material, we usually have these or such for this kind of pointing.
PS:
Additionaly, i feel it should have been PCBs and not PCB's, which however, is a non-issue here since it is not in the underlined portion.
