Question

experimental research is concerned with all of the following groups, except for which of the following? placebo group control group sub - populations experimental group

Explanation:

Experimental research relies on comparing groups to test variables: the experimental group receives the treatment, the control group does not, and a placebo group gets an inert treatment to control for psychological effects. Sub-populations are broader segments of a population, not a specific group designed for experimental manipulation or comparison in this framework.

Answer:

C. Sub-populations