Which of the following statements correct describes a double-blind experiment?
a. Both the test subjects and the researchers in direct contact with them know
who is in the experimental group and who is in the control group.
b. The test subjects but not the researchers in direct contact with them know
who is in the experimental group and who is in the control group.
c. The researchers in direct contact with the test subjects, but not the test
subjects, know who is in the experimental group and who is in the control
group.
d. Neither the test subjects or the researchers in direct contact with them
know who is in the experimental group and who is in the control group.