The answer to your question would be that the best source to use to find the pronunciation of the word "etymologists" is the dictionary. That is, your answer would be A.
Dictionaries contain a collection of words and their definitions and sometimes other information, such as the origin of words and their pronounciation. However, there are dictionaries of pronounciation in which you can only find the pronounciation of the word you are looking up to, not its definition.
