Industrial pollutants

[BlueDragon2010]

The industrial pollutants known as PCB's were first manufactured in 1929 and were used as coolants for electrical equipment in Europe and North America until the 1970s, when studies showed that the compounds had entered the food chain and were harmful to some animals.

(A) that the compounds had entered the food chain and were harmful to some animals

(B) the compounds to have entered the food chain and be harmful to some animals

(C) the entry of the compounds into the food chain as harmful to some animals

(D) the entry of the compounds into the food chain and its harmfulness to animals

(E) the compounds entering into the food chain and harming some animals

[Patrick_GMATFix]

The precise meaning intended is that the study shows that compounds had entered the food chain and that those compounds were dangerous. Eliminate sentences saying that the study showed the compounds entering the food chain, or that the study showed the entry of the compounds into the food chain. These are imprecise in meaning. The full solution below is taken from the GMATFix App.



-Patrick

[[email protected]]

Hey!
Option "A" breaks parallelism.
showed that .. past perfect and simple past.
I don't UNDERSTAND, am I missing something?

Regards,
Mukherjee
EXPERTS Do HELP

[neptune28]

Hey!
Option "A" breaks parallelism.
showed that .. past perfect and simple past.
I don't UNDERSTAND, am I missing something?

It can be easy to overthink some of these questions, and this is one of them. This sentence is actually pretty simple.

Choices B) - E) are all awkward and/or unidiomatic.

Choice A) does not really have anything to do with parallelism. What if you said:

The compounds had entered the food chain and had been harmful to some animals?

That would imply that the compounds were no longer harmful. But why would that be the case? Once harmful, pollutants are always harmful, unless you can find a way to get rid of them. It is not correct to assume that you can never use the past perfect and past tenses together.

Here's a case in which mixing the tenses would be incorrect:

I knew that she had visited my parents and gave them all the information on where I was last Friday night.

Hope this helps, Mukherjee.