The correct answer is option 4: Large intestine. Roundworm is a type of human parasite that commonly resides in the large intestine. The large intestine, also known as the colon, is the final part of the digestive system where water is absorbed from the remaining indigestible food materials, and the formed waste is eliminated from the body. Roundworms, scientifically known as nematodes, can infect humans by ingesting their eggs or larvae through contaminated food, water, or soil. Once inside the body, the roundworms reach the large intestine where they mature and reproduce. This can lead to various symptoms and health problems, including abdominal pain, diarrhea, and nutritional deficiencies. Therefore, it is important to practice good hygiene and proper food handling to prevent roundworm infections.