Antecedent of a pronoun is a word that the pronoun refers to, or replaces. So, in this sentence, we are looking for the antecedent of the pronoun IT. The pronoun IT replaces the noun Chicago, which means that the word Chicago is the antecedent of the pronoun IT.
IT provides the best opportunity, meaning that Chicago does that.
The correct answer is B, a social class. 'Interest groups' have the same interest that influences them. "A political party' is about politics. And D isn't correct as this is not a culture, it is merely a class.
An allusion is an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.
