Answer: Solomon four group
Explanation:The Solomon four-group design is known to have:
Pretest, post test, treatment and no treatment. It is also known as the best. It reduces threats to internal and external validity and controls the effects of the reactive of pretest.
The Solomon four group design is made in a pretest and posttest two-group design and the posttest in an only control design. The tested and untested groups
combinations with a treatment and a control groups helps one to understand and know the mix-up variables and other irrelevant factors alter not the result.