Just to clarify: this holds when you have a pronoun subject in the 2nd clause, not just any old pronoun at all. Also, it doesn't mean that you MUST refer to the noun subject of the first clause - it just means that you woudl most often expect it to structurally, so if that noun subject is an actual match in terms of singular or plural, then you have to consider that noun subject a possible antecedent. If there's another, logical match in the sentence, then you have ambiguity (ie, more than one noun that could be the antecedent, either logically or structurally) and that's a problem.
In the example you've given, "they" is not a problem. Logically it refers to "consumers." Structurally, it would refer to "price," which is not plural... so "they" is not a candidate to refer to "price." No ambiguity is created (there's only one noun that matches in terms of number), so it's fine.
I did a search to see if I could find the source of the problem. I didn't get a definitive answer but it seemed to come from the 1000 SC sets. I also found another site which claimed the official answer was D, not C.
1000SC has many good questions, but it also has some downright bad ones, including problems on which the right answer has errors in it, and the official answer is wrong. It is a mix of old paper and pencil questions and apparently either bad questions from other sources, or errors introduced into good questions via transcription. The problem is: you don't know which ones are good and which are bad,
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