The correct answer is B. 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 a heme group. The heme group is a complex of iron and protoporphyrin IX, which is a ring of four pyrrole rings. The iron in the heme group is able to bind to oxygen, and this is how haemoglobin carries oxygen in the blood.
Insulin is a hormone that is produced by the pancreas. It helps the body to use glucose for energy. Gastrin is a hormone that is produced by the stomach. It helps the stomach to produce acid and digestive enzymes. Actin is a protein that is found in muscle cells. It helps the muscles to contract.
Haemoglobin is the correct answer because it is the only option that is an oxygen carrying protein. Insulin, gastrin, and actin are not oxygen carrying proteins.