What industry first led to a breakthrough for the Cincinnati Mill Company?

The correct answer to this open question is the following.

Although there are no options attached or further references, we can say the following.

The industry that first led to a breakthrough for the Cincinnati Mill Company was the new technology machine-building industry in the United States.

Located in Cincinnati, Ohio, the Cincinnati Milling Machine Company was the first industrial company to fabricate milling machines to cut surfaces removing unnecessary materials. Two innovative businessmen and industrial people were at the forefront of this company: Fred Holtz and Frederick A. Geier, who opened the fabric in 1889.

the answer is c.

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