Which Scenario Best Describes a Double-Blind Study

Multiple Choice

Which scenario best describes a double-blind study?

A) The investigator and the subjects wear blindfolds.
B) No one knows what is in the experimental or control group
C) The subjects do not know if they are in the experimental or control group.
D) Neither the investigator or the subjects know if they are in the experimental or control group.
E) The investigator does not know if subjects are in the experimental or control group.