This question tests the ability to understand analogical relationships.

Analogy Reasoning

The relationship between "Forest" and "Trees" is that a forest is composed of many trees. Trees are the fundamental components that make up a forest.

Applying this logic to "Book", we need to find the component that makes up a book.

Option Analysis

• Pages: A book is fundamentally composed of pages. This matches the relationship (Forest: Trees :: Book: Pages).
• Bind: Binding is a process used to assemble a book, not a component itself.
• Writer: A writer creates a book, but is not a component part of the book's structure.
• Pen: A pen is a tool used for writing, unrelated to the components of a finished book.

Therefore, "Pages" is the word that completes the analogy.