The correct answer for the highest source of protein is option 2 - Soybean. Soybean is considered to be one of the best sources of plant-based protein. It is rich in essential amino acids and provides a complete protein profile. Sunflower seeds, option 1, and grams, option 3, also contain protein but in lower quantities compared to soybean. Wheat, option 4, is a carbohydrate-rich grain and does not contain as much protein as soybean. It is important to note that there are other sources of protein as well, such as animal products like meat, fish, and dairy. However, if we focus on plant-based options, soybean stands out as an excellent choice for protein intake.