Which packaging innovation in the 1930s revolutionized book accessibility and created what is often called 'the paperback revolution'?

The way books are packaged and presented has evolved dramatically over centuries, influencing both their accessibility and cultural impact. From ancient scrolls to modern paperbacks, packaging innovations have shaped how we interact with literature. This trivia question explores a pivotal moment when packaging transformed the literary landscape and democratized reading. Test your knowledge of how the physical presentation of books changed literary consumption patterns!

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Penguin Books' standardized paperback format with color-coded covers priced at sixpence (the cost of a pack of cigarettes)
Random House's 'Modern Library' series with dust jackets and embossed covers
Doubleday's introduction of spiral-bound books with protective cellophane covers
Simon & Schuster's 'Pocket Book' collection with leather-like covers and gold lettering