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

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

[email protected] wrote: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.