When was . . . . . . . . paper first made?

Answer: Option D

When was paper first made?

In this context, "paper" is a general, uncountable noun referring to the material itself, rather than a specific piece of paper. Therefore, it does not require an article.

Option A: a is incorrect because "a" is used for singular countable nouns, and "paper" in this case is uncountable.

Option B: an is incorrect for the same reason as above; "an" is used before words starting with a vowel sound for singular countable nouns, which does not apply here.

Option C: the is incorrect because "the" indicates specificity. Since we are discussing paper in general, not a specific type or piece of paper, no article is needed.

Conclusion: The correct answer is Option D: no article, as it appropriately reflects the use of "paper" as a general, uncountable noun in this context.