An example of grain legume is

Grain legumes are a group of crops that are grown for their edible seeds, which are high in protein and other nutrients. Legumes are also important because they can fix atmospheric nitrogen into the soil, which helps to improve soil fertility. Out of the given options, pigeon is an example of a grain legume. Pigeon pea, also known as red gram, is a widely cultivated legume crop that is grown in many parts of the world, particularly in South Asia and East Africa. The seeds of pigeon pea are a rich source of protein, and the crop is also used as a forage for livestock. Maize, sorghum, and millet are not examples of grain legumes. Maize and sorghum are both cereal crops that are grown for their edible grains, while millet is a small-seeded grass that is grown as a cereal crop in many parts of the world. While these crops are important sources of food and feed, they are not classified as grain legumes.