The correct option is
A Caused by substitution of valine by glutamic acid in the
β-globin chain of haemoglobin
Sickle-cell anaemia is caused by a change in a single base pair of DNA (substitution of valine by glutamic acid in the β-globin chain of haemoglobin). It is a genetic disease. The individuals suffering from sickle-cell anaemia are immune to malaria. Thus, option B is correct.