2. Prior to its development, books were manually transcribed and exceptionally scarce. (Establishes the historical backdrop preceding the central innovation. "Its" refers to the printing press.)
1. The printing press dramatically transformed information distribution. (Introduces the invention and its principal consequence.)
4. With books becoming more affordable and obtainable, readership expanded. (Details the direct outcomes of the transformation in point 1, elucidating the mechanism of information dissemination change.)
3. This advancement ultimately fostered widespread literacy. ("This advancement" refers to the printing press and its ramifications. Widespread literacy represents a broader, enduring societal effect of increased readership.)
This order presents a coherent progression from the era before the invention, through the invention itself, its immediate repercussions, and finally its extended societal influence. (Note: Option (d) is identical to (a)).