When Social Scientists Conduct Interviews, It Is Required by the Ethics

When social scientists conduct interviews, it is required by the ethics of the field that the social scientist receives "informed consent." What is "informed consent"?

A) when funding agencies give the "go ahead" to begin the research that is being funded
B) getting permission from other researchers to use non-random sampling
C) getting permission to conduct the interview after having given the respondent some information about research/interview
D) getting permission to talk to respondents about their sexual behaviors