Final answer:
Corn and barley are the two grains commonly used to make up the rest of the mash in American rye whiskey production. Whiskey's importance in American history is highlighted by events such as the Whiskey Rebellion and its medicinal use during Prohibition.
Step-by-step explanation:
American rye whiskey must contain at least 51 percent rye mash, with the remaining mash usually consisting of other grains to complete the fermentation process. Among the options provided—corn, barley, wheat, oats—the other two grains that commonly make up the rest of the mash in rye whiskey production are corn and barley. Wheat and oats are less commonly used. These grains, along with the unique water sources such as the naturally filtered spring water in the karst regions of Kentucky and Tennessee, contribute to the distinct flavors of various whiskeys.
Rye whiskey has been a significant part of American history. It served as a frontier staple, preserving the harvest, which led to the event known as the Whiskey Rebellion in 1794 after a tax was imposed on whiskey. Furthermore, state and local ordinances have allowed for whiskey to be prescribed as "medicine," reflecting its entrenched role in American society.