What machine is used to separate cotton fibers from the seeds?

The cotton gin is a machine specifically designed to separate cotton fibers from the seeds. This process is crucial in cotton production as it enables the harvesting of the valuable fibers that can be spun into thread and fabric. The cotton gin works by using a series of saws and brushes to pull the fibers away from the seeds efficiently, which significantly speeds up the production process compared to manual methods.

In the context of agriculture, the cotton gin revolutionized the cotton industry by allowing for large-scale processing of cotton, which in turn increased availability and reduced costs. This innovation is particularly significant because, before the cotton gin's invention by Eli Whitney in the late 18th century, separating fibers from seeds was a labor-intensive and time-consuming task.

The other options represent machines used in different agricultural contexts or processes. A threshing machine is used to separate grains from the straw and chaff after harvesting, a harvester is a broader category of equipment used to gather crops from the fields, and a Smith machine is a type of weight training apparatus with no relevance to agriculture or cotton processing.