What Does It Meant to Say That a Study Is

What does it meant to say that a study is "double-blind"?

A) Each patient receives both the drug being tested and a placebo,so that the effects of the drug can be compared to the effects of the patient's expectations.
B) While the patient is aware to what treatment he or she is receiving,his or her family,friends,and therapist are not.
C) Both the patient being given the drug and whoever will evaluate the drug's effects do not know whether the patient was given the treatment or the placebo.
D) Two conditions are used,a treatment and a placebo.