A child aged 2 year presents with nonspecific symptoms suggestive of anemia.On peripheral blood smear target cells are seen.He has hypochromic microcytic picture and Hb of 6gm%.He also has 'a positive family history'. Next investigation of choice is

• A. Liver function tests
• B. Osmatic fragility test
• C. Hb electrophoresis
• D. Coombs test