Sentence Correction (SC) | Re: In the mid-1970s, since birds were overcome by pollution, and routinel

Hellopikolo2510 ,

Thank you for your query.

Yes, on GMAT SC, it is a rule that demonstrative pronouns must be followed by the noun they refer to.

For example:

I found an old pen in the attic; this belonged to my great grandfather. ---> Incorrect
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