The correct answer is A. haemoglobin. Haemoglobin is a protein found in red blood cells that carries oxygen from the lungs to the rest of the body. It is made up of four subunits, each of which contains an iron atom. The iron atom binds to oxygen, and the haemoglobin molecule carries the oxygen to the tissues.
Keratin is a protein found in hair, nails, and skin. It is a tough, fibrous protein that helps to protect these structures.
Collagen is a protein found in bones, skin, and tendons. It is a strong, flexible protein that helps to provide structure and support to these tissues.
Myoglobin is a protein found in muscle cells. It stores oxygen and releases it to the muscle cells when they need it.
In conclusion, the correct answer is A. haemoglobin. Haemoglobin is a protein found in red blood cells that carries oxygen from the lungs to the rest of the body.