While I'm not entirely sure what this question is expecting of you, I can help.
A={4,7,10,13,17} B={3,5,7,9}
If you were to find the union, it would be: {3,4,5,7,9,10,13,17}
If you wanted to find where these two INTERSECT, then it would definitely be 7
It looks to me, if that is what your first choice is saying, that it's the first option: A U B=7. But I am unfamiliar with some of these terms, so if this ISN'T what option A is saying, then don't go with it.
But from my knowledge, it looks like the first choice is correct.
~Hope this helps m8