Consider the following statements about haemoglobin:
1. It carries oxygen in the blood.
2. It is an iron-containing compound.
3. It provides immunity against certain diseases.
4. It imparts red colour to the blood.
The correct statements out of these are:

1. A.1, 2 and 3
2. B.1, 3 and 4
3. C.2, 3 and 4
4. D.1, 2 and 4