Which one of the following CANNOT be said about the history of immunity:
A) the ancient Greeks knew something existed within the body to protect it from infectious disease
B) scientists of the 1800s discovered "factors" now called antibodies
C) scientists of the 1800s demonstrated that immune serum could protect another animal from disease
D) scientists of the mid-1900s discovered the viral origin of AIDS
E) scientists of the mid-1900s discovered that injection of serum containing antibodies did NOT always protect a recipient from disease
Answer: D