Neilsheth2 wrote:Hey Mitch you precisely write that the 'IT' in answer' A 'can not refer to the THE FIRST BIRTH in the preceding modifier? is it because the preceding clause is a noun modifier? the modifier making it must refer to the main clause?

I chose A since I though it may refer to the first birth- implying ---> making the first birth a landmark development...!!

A Sumatran rhinoceros was recently born in a Cincinnati zoo, the first birth in captivity of that species in more than a century, making it a landmark development for the effort to save the endangered animal.

Generally, the antecedent for a subject pronoun (he, she, it, they) or an object pronoun (him, her, it, them) should be a noun or nouns in the preceding MAIN CLAUSE.
The antecedent should NOT be a noun in a non-essential modifier.
In A, the portion in red is a NON-ESSENTIAL MODIFIER.
For this reason, it is inappropriate for it to serve to refer to the first birth (a noun in a non-essential modifier).

Even if we interpret that it refers to the first birth, the meaning conveyed by A is nonsensical, since the agent of making must be a Sumatran rhinoceros (the preceding subject).
Conveyed meaning:
A Sumatran rhinoceros was MAKING THE FIRST BIRTH a landmark development.
Not the intended meaning.
Eliminate A.