Which of the following statements are correct regarding structure and types of antibodies in humans?
i. Antibodies are also called Immunoglobulins that are produced as an immune response to antigenic stimulation.
ii. They are produced by all types of T-lymphocytes and B-lymphocytes.
iii. Antibody is an 's' shaped molecule formed of six polypeptide chains. Antibodies present in plasma determine many blood group systems like ABO, Rh, P, MNS etc.
iv. Antibody molecule consists of two antigen binding sites called paratopes.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.