Xenophobia is the hatred or fear of strangers or unusual circumstances/objects. Let us take a look at the provided answers and see which provides the best comparison:
A. hydrophobia : sharks
Hydrophobia is the fear of water. Sharks aren't water, but they live in water. The comparison doesn't exist, so we can move on.
B. bibliophilia : books
Bibliophilia is the love of books, and while there is a bit of a comparison, it is more or less the opposite of the original comparison.
C. acrophobia : heights
Acrophobia is the fear of heights, so there is a definite comparison here with the original. This is most likely correct, but let us examine the last answer anyway.
D. philanthropy : charity
Philanthropy is the compulsion to give money or valuables away to others who may want/need them more than you. In this case, philanthropy and charity are synonyms, so there isn't a real clear comparison to be made.
So your final answer is:
xenophobia : foreigners :: acrophobia : heights
C is your correct answer choice.
Hope that helped =)