Which classic novel became a bestseller largely due to its innovative "whisper campaign" marketing strategy where the publisher hired people to discuss the book loudly on public transportation?

Before the age of digital marketing and social media influencers, classic literature had its own promotional innovations. Some marketing campaigns for books were so revolutionary they changed publishing forever. This trivia question explores one of the most influential marketing strategies in literary history that transformed a good book into a cultural phenomenon.

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Jacqueline Susann's 'Valley of the Dolls' (1966)
J.D. Salinger's 'The Catcher in the Rye' (1951)
Margaret Mitchell's 'Gone with the Wind' (1936)
Joseph Heller's 'Catch-22' (1961)