when neither the participants nor the experimenters know which group has received the treatment and which has received a placebo, the design is called . confounding. b. double-blind. c. correlational. d. naturalistic. e. retrospective.

The correct answer is option B. double- blind.

Explanation:

A single blind study or experiment, in which there is participants do not know the what treatment get during the experiment while the experimenters know about the treatment and records data.

In double blind study or research it is a design there is neither experimenters nor the participants know what experimental treatment is given or which when is given control treatment or received a placebo.

Thus, the correct answer is option B.