Why Was the Study of Black Sharecroppers with Syphilis a Controversial

Why was the study of black sharecroppers with syphilis a controversial study?

A) the entire study sample was poor black men in the South
B) the participants were offered free medical care, meals, and life insurance to cover burial costs, but were not given the promised rewards
C) one-third of the study's participants did not have syphilis at the outset of the study but were given syphilis through the study
D) during the study, a treatment for syphilis was discovered but was not given to the study's participants, resulting in continued suffering and death from the disease