Answer the following question: Answer the following question given this paragraph: The trillions of red blood cells in blood plasma carry oxygen. Red blood cells contain hemoglobin , a protein with iron that binds with oxygen. Red blood cells are made in the marrow of long bones, rib bones, the skull, and the vertebrae. These cells survive for about 120 days, and then they are destroyed. Mature red blood cells lack a nucleus and other organelles, allowing for more hemoglobin, and therefore more oxygen to be carried by each cell. Q: What is the protein that carries iron that binds with oxygen in red blood cells? A:

Available choices:
+ keratin;
+ potassium;
+ insulin;
+ hemoglobin;
Answer:
hemoglobin