Which of the following refers to the course grains?

The term "course grains" typically refers to cereal grains used primarily for animal feed or as staple food sources for humans and livestock. In the given options, corn, grain sorghum, and soybeans are indeed classified as coarse grains due to their role in agriculture and their use in various food products.

Corn is the most widely produced grain in the United States and is significant in animal feed as well as human consumption. Grain sorghum, likewise, serves similar purposes, thriving in arid conditions where other grains may struggle. While soybeans are primarily known for their oil and protein content, they play a crucial role in the livestock industry as well, categorized under coarse grains when focusing on their agronomic aspect.

The other options contain grains that are not classified as coarse grains. Wheat, barley, and oats (first option) are considered cereal grains but do not fall under the category of coarse grains as commonly understood in agricultural contexts. Rice and millet (second option) are also important grains but are more often classified as fine grains. The last option includes root vegetables, which are entirely different from grains in both classification and usage. Therefore, the correct selection here accurately represents the commonly accepted definition of coarse grains in agricultural practices.