Answer: D) Encyclopedia.
Explanation: To know which kind of reference book is better to find information about solar energy, we need to know what is the purpose of every kind of reference book. An almanac is a publication containing astronomical and meteorological data for a given year and often including a miscellany of other information, an atlas is a book of maps or charts, a thesaurus is a book that lists words in groups of synonyms and related concepts and finally, an encyclopedia is a book or set of books giving information on many subjects or on many aspects of one subject, so the correct answer is option D: an encyclopedia.
