Which word says complete the analogy

Core:apple::

A. orange : peel

B. chorus:choir

C. nucleus : atom

D. hour:clock

A because B is practically the same, which is not the case for the analogy above, and its not C because the atom has a different relationship with the nucleus, which is different from the relationship between the core and the apple. Lastly, its not D because the clock simply relates the hour, but the hour does not make the clock what it is, and they have no important relationship. This leaves only A, in which the orange acts as the "core", while the apple acts an outside covering, or the "peel".

Orange:peel (a) because nothing else has to do with fruit or underneath.