Answer:
c. it causes red blood cells to distort which makes them less hospitable to Plasmodium, the parasite that causes malaria
Explanation:
The normal haemoglobin is a tetramer of four globin chains (2 alpha and 2 beta chains).
When a gene mutation occurs, i.e the substitution of a single nucleotide which leads to the formation of valine instead of glutamate, the hemoglobin would become sickle shaped. This gives rise to the Hb S allelle.
Therefore in malaria-endemic regions, the S allelle is beneficial because the distorted or sickle-shaped red blood cells would be less hospitable to Plasmodium and this would confer protection on the host.