Which statement is an example of a complete analogy? a pen is like a mind reader. my cousin is like a whirlwind; she arrives out of nowhere, leaves a mess, and disappears. our road trip was like a long trip on a broken-down magic carpet. an atom is like the solar system.

An analogy is a comparison of two things that may be quite different from each other, but the statement explains that idea or thing by comparing to something familiar. Therefore, the only complete idea is the second option:

My cousin is like a whirlwind; she arrives out of nowhere, leaves a mess, and disappears.

Because the author is trying to say that his cousin does not behave well, he always makes a mess in the house and then instead of cleaning the disaster he made, he leaves. Then it is easy to find it similar to a whirlwind, because it is also unexpected and causes a disaster that someone else has to clean.  

moon-letters were a method of writing invented by the dwarves. moon-letters were ordinary runes, but written in such a way that they could only be read when the light of the moon shone behind the writing. some moon-letters could be read by any moonlight, but it was possible to make the writing even more secret. more sophisticated moon-letters could only be read by the light of the same shape of moon, or at the same time of year, as when they were written. hope this !