I don't think "it" is referring to anything in A.
This is one of the cases where "it" does not have any antecedent.
E.g. It is raining outside.
In the above sentence "it" has no referent.
As to the question of what is being tested, I am not too sure. Since A is correct,probably what the testers want to test is if we can understand that "it" can be used without referring to any pronoun.
Also, the other answers have very glaring mistakes. The testers are also testing us to see if we recognize the mistakes in the wrong answer choices.
Idioms related to aim(my own notes, you can disagree) :
aim for ( to get tangible things...aim for a gold medal )
aim to ( in the sense of achieving/intending something)
aim at ( point somethign at someone)
aim with ( use something to point to someoen )
I'm crossing the bridge.........