Out of your 3 possible answers, B. ones' is the correct one and I will explain why. Answer A is a contraction of one and is. When you put "one is" into the blank space you can tell that it is not right. Answer C is incorrect because when you place an apostrophe after an s it is implied that there should be another s that follows and so you do not need to put it there. This means that answer B is correct since it doesn't have the extra s.
The information about the Luggnaggians which the narrator
(Gulliver) offers to his audience (English people) is their traditional
customs. At some fact of the story, Gulliver gives his view on the way to
points of views of Luggnaggians by telling it in order to make his spectators
learn the conceivable errors of others and not to do it again.
