HIV/AIDS Can Be Categorized as a New or Emerging Infectious

HIV/AIDS can be categorized as a new or emerging infectious disease.By putting it into this category,we are effectively saying that

A) this infection hasn't been observed in the human population prior to recent (approximately 50 years or sooner) outbreaks.
B) this disease has been in susceptible populations for centuries,but has only recently achieved infection levels that became detectable.
C) the infectious agent is still evolving and changing,unlike with older,more established diseases such as plague or polio.
D) the disease has always been in susceptible populations and causing disease,but we lacked the technology to detect it.