There are no options given, but historically speaking it was the invention of "Cotton Gin".
A cotton gin was a revolutionary invention which enabled people to
easily separate cotton fibers and seeds; previously it used to take a large
time sorting it manually. The inventor behind this was <span>Eli Whitney. The processing was made easy but
still slaves were needed to grow cotton.</span>
Explanation:
I don't understand what your question is I need more information ?
Answer:
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I would go with D. All of the above. Even though I don't know about the Song/Tang Dynasties, I know for sure that they invented those things. So it is D.