The answere is piston because i did this question for my class and that was the answer for me. ;
The first one and the third one both look like good answers. But if I had to choose one, I would go with Piston because its talking about technology. The piston is part of an engine so it would have to do with technology. :)
The best domain-specific term to use in a research essay on Civil War battle technology is "broadside," as it refers to naval tactics employed during the war. While "piston" relates to technology, it does not directly connect to the Civil War. "Patella" is unrelated altogether, being a term from human anatomy.
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