It Has Been Difficult to Generate Drugs to Treat AIDS

It has been difficult to generate drugs to treat AIDS for which reason?

A) The only way to kill a virus is with a vaccine, not with drugs.
B) People with HIV infections die very rapidly, before the drugs have a chance to cure them.
C) HIV does not use any enzymes that can be targeted by drugs.
D) HIV mutates rapidly among infected humans.
E) HIV does not cause AIDS.