Concept:
- Printing spread to Japan from China along with Buddhism, so the first Japanese book has to be a Buddhist text.
- Reading the options against that single test removes three of them at once.
Step 1: Set the test.
Ask of each option two things: is it Buddhist, and is it Japanese. Only a choice that answers yes to both can be the oldest printed book in Japan.
Step 2: Apply the test to the non-Buddhist choices.
The Japanese Bible is not Buddhist, and Ukiyo names a picture style rather than a religious book. Both fail the first half of the test.
Step 3: Apply the test to the two Buddhist choices.
Tripitaka Koreana is Buddhist but Korean, so it fails the second half. The Diamond Sutra is Buddhist and its printed Japanese edition of 868 CE survives, so it passes both.
Step 4: State the reason behind the fact.
Buddhist missionaries carried hand-printing from China into Japan around 768 to 770 CE, which is exactly why the earliest printed Japanese book turns out to be a Buddhist sutra.
Final Answer: (A) Diamond Sutra