Which e-commerce innovation first allowed customers to digitally 'look inside' books before purchase, revolutionizing online literary retail in the early 2000s?

The publishing industry has undergone dramatic transformations in the digital age. From traditional bookstores to online giants, the way we discover, purchase, and consume literature continues to evolve. This trivia question explores a significant innovation in the online book retail space that changed how readers interact with literature. Test your knowledge about the intersection of technology and literary commerce!

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Amazon's 'Look Inside the Book' feature (2001)
Barnes & Noble's 'Digital Preview' service (2003)
Google Books' 'Sample Pages' technology (2004)
Apple's 'iPreview' for iTunes bookstore (2005)