Hmm this is a rather hard question, no choice seems to provide a good explanation.
Basically the paradox says that US people used to travel to Europe a lot because other countries are not open. Now that other countries are open, and they are as safe and as valuable (as full of things to do) and even cheaper, why then we see even more people go to Europe?
Why I first read this question, I thought that the explanation was that people from other countries have been visiting Eruope, for the question stem didn't say more US people are visiting Europe. Unfortunetaly this is not one of the explanations.
(A) U.S. travelers feel at least as safe in Western Europe as they would in the other countries.
So both Europe and other countries are safe. Why would they all go to Europe then?
(B) U.S. travelers recognize the better value of travel to Western Europe.
There isn't a "better value" for travelling to Europe, according to the stem. However if this were true ... then it could explain the paradox. But it can't be true hmmm.
(C) Many airlines would love to acquire exclusive rights to offer flights to some Western European countries.
This one is rather interesting. On the surface if they have exclusive rights the airline tickets may have been more expensive, compare to other countries where many airlines are competing. In other words, people should have gone to Europe less often ... But let's keep this one for a little bit ...
(D) At one point in time, it was much more difficult to arrange travel to non-Western European countries.
So now it's easier to travel to non European countries. Why then do more people travel to Europe?
(E) The governments of Western European countries are very concerned with having Americans travel there, so they sometimes transfer the advertising of their country`s merits to other advertising firms.
This one again is curious. I'm not sure why the first part of the sentence would lead to the second part. However if they do let other advertising firms advertise for them, perhaps those firms do this very successfully and that's why people go to Europe more often?
Well, given that B and E are not correct, I would guess C, for A and D seem to me rather incorrect. From C, we could say that they love to get the exclusive right but they may not have gotten it, and so they may actually compete even harder for it, and therefore airline tickets are cheaper so more people go there ... I know it is a little far fetched.
Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.