Final answer:
The Diamond Sutra, dating back to 868 C.E., is recognized as the world's first block-printed book, used for spreading Buddhist teachings and representing a major advancement in text production. Option D is correct.
Step-by-step explanation:
Dated to 868 C.E., scholars believe that the Diamond Sutra represents the world's first block-printed book.
It was used as a means to disseminate Buddhist teachings more broadly, which illustrates the significant cultural and technological advancement in the production of texts during that period. This early form of mass-produced literature paved the way for greater distribution of knowledge and religious doctrine, which was previously limited by the labor-intensive process of hand-copying texts.
Therefore, the correct answer to where this work was first used is D. Printed book.