Final answer:
An encyclopedia (c) is designed to provide additional knowledge and understanding to readers, offering comprehensive overviews on a wide range of topics, unlike novels, textbooks, or dictionaries.
Step-by-step explanation:
The item described as 'Its sole purpose is to give additional knowledge and understanding to readers' is best represented by (c) An encyclopedia. An encyclopedia provides basic information, explanations, and definitions on a wide range of topics. Unlike novels which are primarily for entertainment and engaging the imagination, textbooks which focus on a specific subject matter for educational purposes, and dictionaries which define the meanings of words, an encyclopedia serves as a general reference that offers a more comprehensive overview of various subjects. Encyclopedias such as the New Encyclopædia Britannica offer in-depth information, whereas single-volume works give brief overviews useful in gaining background information and basic facts about virtually every topic.