Which of the following sources would be most helpful for a writer who is trying to find some interesting facts on whales and porpoises?

Question

Quizplus · Accepted Answer

An encyclopedia is a book or set of books giving information on many subjects or on many aspects of one subject and typically arranged alphabetically.
Dictionary is incorrect. A dictionary is a book that shows the proper spellings and definitions of words. 
Thesaurus is incorrect. A thesaurus is a book that lists words in groups of synonyms and related concepts.
Style guide is incorrect. A style guide is most useful for determining proper punctuation. It contains a set of standards for the writing and design of documents.

Which of the Following Sources Would Be Most Helpful for a Writer