[填空题]

[A] The strain of HIV that was discovered in Sydney intrigues scientists because it contains striking abnormalities in a gene that is believed to stimulate viral duplication. In fact, the virus is missing so much of this particular gene-known as nef, for negative factor--that it is hard to imagine how the gene could perform any useful function. And sure enough, while the Sydney virus retains the ability to infect T cells--white blood cells that are critical to the immune system’s ability to ward off infection--it makes so few copies of itself that the most powerful molecular tools can barely detect its presence.
[B] If this speculation proves right, it will mark a milestone in the battle to contain the late-20th century’s most terrible epidemic. For in addition to explaining why this small group of people infected with HIV has not become sick, the discovery of a viral strain that works like a vaccine would have far-reaching implications. "What these resul