The correct answer choice (C) is the most parallel so I get that but why is "it" not ambiguous (as per GMAT's standards) between Radio and Telephone? Is there a rule we should be aware of i.e. if X is clearly the subject in the first clause, the pronoun in the succeeding clause can refer to X even when there are other nouns in the first clause that could be referred by that pronoun?
There is another question in the new OG that had the same issue [deleted by moderator]
Thank you for your help on this!