The analogy between "Chocolate : Sweet" and "Encyclopedia : Book" can be explained as follows:

1. Understanding the analogy:
In order to understand the analogy, let's first analyze the relationship between "Chocolate" and "Sweet." Chocolate is a type of food that is known for its sweet taste. Therefore, "Sweet" can be considered a characteristic or quality of chocolate.

Similarly, when we consider the relationship between "Encyclopedia" and "Book," an encyclopedia is a type of book that contains information on various subjects arranged alphabetically. Therefore, "Book" can be considered a category or classification of an encyclopedia.

2. Identifying the relationship:
The relationship between "Chocolate" and "Sweet" is that of a characteristic and the object possessing that characteristic. Chocolate is characterized by its sweetness.

Similarly, the relationship between "Encyclopedia" and "Book" is that of a category and the object belonging to that category. An encyclopedia falls under the category of books.

3. Applying the analogy:
Based on the relationship identified, we can apply the analogy to determine the correct answer. Just as chocolate is characterized by its sweetness, an encyclopedia is characterized by its format, which is a book.

Therefore, the correct answer is option B) Book, as it represents the relationship between "Encyclopedia" and "Book" similar to the relationship between "Chocolate" and "Sweet."

4. Eliminating other options:
a) Dictionary: While a dictionary is also a type of book, it is not the most appropriate answer as it does not capture the specific relationship between "Encyclopedia" and "Book" in the given analogy.

c) Library: A library is a place where books are stored and accessed, but it does not represent the relationship between "Encyclopedia" and "Book" as closely as option B.

d) Composition: Composition refers to the act of creating or writing something, and it does not fit the analogy or relationship between "Encyclopedia" and "Book."

Conclusion:
In conclusion, the analogy between "Chocolate : Sweet" and "Encyclopedia : Book" can be explained by the relationship between a characteristic and its object or a category and its belonging. Therefore, the correct answer is option B) Book.