Hi, I believe (if I recall this kind of exercise correctly, I'll have to track down my notes) the three sentences have approximately the same meaning.
In this case, look at section B of the lesson for this unit:
The participle can be translated into English with causal ("since"), concessive ("although"), temporal ("when", or conditional "if") force. The participle alone, then, can stand for the if-clause (protasis) of a conditional sentence.
this was what might be going on here given the content of the sentence (i.e., the reference to the Aeneid
), but I didn't want to answer you until I had a chance to check. This is a fairly common construction in Greek with the relative pronoun.