All of the Following Are Reasons Why an HIV Vaccine

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

A) there is no known animal model of natural immunity for HIV infection.
B) use of a weakened virus would potentially transmit the infection.
C) small,inexpensive animals which could be used for HIV 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.