How Does the Case of Sickle Cell Disease and Malaria

How does the case of sickle cell disease and malaria illustrate a potential complication of germ-line gene therapy?

A) Malaria is not controlled by one single gene.
B) The gene that controls malaria also controls red blood cells.
C) Removing the sickle cell gene prevents sickle cell disease, but it also prevents the development of red blood cells.
D) Having one sickle cell gene doesn't cause a severe version of the disease and it also makes a person resistant to malaria which is important for those living where malaria is prevalent.
E) A person with two sickle cell genes is resistant to mosquito bites which carry malaria, a disease worst than sickle cell.