Answer:
I think it's b
Explanation:
altho I don't know what the sentence your replacing or the article but b looks like a good choice
3D printing uses computer-aided design (CAD) to create three-dimensional objects through a layering method. Sometimes referred to as additive manufacturing, 3D printing involves layering materials, like plastics, composites or bio-materials to create objects that range in shape, size, rigidity and color.
The President is impeached for the violation of the Constitution.
Answer: first appearances of gunpowder artillery
Explanation: