Google search has more than clues - it has
answers[
^]
I'm sorry, but if you can neither answer the question, nor determine the answer from a google search; and if you haven't got the nouse to say "I don't know the answer - I would examine the execution plan to work out the difference in performance" then I have to question how you got as far as the "interview" in the first place.
Sometimes the "right" answer is to say "I don't know ... but this is how I would find out/remind myself/look it up in the documentation"... that is the best advice I was given, so I'm passing it on to you