In this sentence, what is the antecedent of the pronoun it? although it was old and needed a lot of work, carla knew this was the house for her. a. carlab. workc. housed. her

The pronoun "it" is the antecedent to the word "house" because it makes reference to it. We can state so since personal pronoun "it" refer only to objects and animals or babies to whom we are not emotionally attached.  

It is important to note that the pronoun it is before its co-referential word but we can note how in all fairness the word "house" is the antecedent of the pronoun "it" when we rephrase the sentence in the following way::

Carla knew this was the house for her even though it was old and needed a lot of work.

a. the man as a ruler