Which of the following words is in the language of the grammar G?
This is what we have at our hand.
Now let us see what can be get from the second production in red.

From the production in Blue we have

And the parsing can be stopped using $S\rightarrow \epsilon$
So from the above two work outs we find that the $a$'s and $b$'s are properly nested. (and can be mapped to the problem of valid parenthesization )
That being said let us work the options out:

Alternatively, during the examination, it is hard to get this detailed thought in mind, so one can try to draw the parse tree for any one of the words, trying to do so, you shall get the intuition of the semantics of the language of the grammar.