When Oprah Winfrey selected a title for her Book Club, what was the average sales increase experienced by that book?

Before social media influencers, there was 'The Oprah Effect' - one of the most powerful endorsement phenomena in literature and publishing. When Oprah Winfrey selected a book for her Book Club, the impact on sales was legendary. This trivia question explores the remarkable economic power of perhaps the most famous literary endorsement system in modern history.

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An increase of approximately 20,000-30,000 copies
An increase of approximately 70,000-100,000 copies
An increase of approximately 400,000-600,000 copies
An increase of approximately 1-1.5 million copies