Task: Question Answering
Input (English): Background Paragraph: The primary role of red blood cells in the circulatory system is to transport oxygen to the tissues. The actual carrier of oxygen molecules is the protein hemoglobin, which binds to the oxygen and moves it throughout the body, releasing it in areas where the concentration of dissolved oxygen is low. A certain mutation in the gene for hemoglobin causes a slight change in the structure of this crucial protein, resulting in a disease called sickle-cell anemia. For people with this mutation, the hemoglobin produced by their red blood cells has a tendency to clump together, distorting the shape of the red blood cells and giving rise to the crescent-shaped cells seen above. By understanding the changes in structure that are the underlying cause of this disease, we have developed various ways to treat and manage this illness. 
Story: Dr. Bill studies 2 groups of patients, group S composed of individuals with siclke-cell anemia, and group N with normal blood and no health issues. 
Question: Which group had people with a certain gene mutation?
Output (English): group S.