All of the Following Are Reasons Why an HIV Vaccination

All of the following are reasons why an HIV vaccination has not been developed EXCEPT

A) use of a weakened virus would potentially transmit the infection.
B) there is no known organism that can provide a model of natural immunity.
C) small and inexpensive animals for vaccine research are not available.
D) vaccines are not effective against viral infections.
E) HIV has a high mutation rate so one vaccination would not be effective to treat the world- wide pandemic.