hi, the passage tells us that we can not have a perfect understanding of classical languages. The reason for this is that we cannot directly observe them, which they then use an analogy to demonstrate- one can go to France and hear French, but you cannot go to Ancient Greece and hear Ancient Greek.
This claim, that you cannot go back to Ancient Greece, shows by analogy how modern and classic languages are dissimilar.
In other words, it is an example that contrasts the two things, which supports the conclusion that they are different.
While I am not exactly sure what it means to "point up by example," this is an example that does exactly what B says, regardless of any pointing up.
