A neuron is a nerve cell that is the basic building block of the nervous system.
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.
George Herbert, "The Collar" - cacophony
John Donne, Sonnet 10 - paradox
John Donne, "The Sun Rising" - hyperbole
Andrew Marvell, "To His Coy Mistress" - carpe diem
John Donne, "The Flea" - synecdoche