What symbolic element is featured in Dictionary.com's logo that represents its function as a language resource?

Dictionary.com is one of the world's leading digital language resources. Its logo contains a distinctive element that represents the company's mission to clarify language and make meaning accessible. This poll tests your knowledge about this famous linguistic brand's visual identity and how it communicates the essence of language services through design elements. Can you identify the correct symbolism behind their iconic logo?

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A speech bubble containing the letter 'D', representing dialogue and definition
An open book with the letter 'D' on its page, symbolizing knowledge and reference
A magnifying glass over the letter 'D', indicating search and discovery
A quill pen forming the letter 'D', representing writing and etymology