In What Way Could the Researchers in the Willowbrook Study

In what way could the researchers in the Willowbrook study have designed their research on the hepatitis virus so that it was ethically acceptable?

A) The researchers could have given each participant a chance to assent.
B) The researchers could have performed their study on persons who were capable of full assent.
C) The researchers could have made the study available at many institutions for the mentally retarded.
D) The researchers could have performed descriptive research on persons already infected with hepatitis.