A Researcher Tests the Effects of a Skills Enhancement Program

A researcher tests the effects of a skills enhancement program by measuring the change in social adjustment of a group of handicapped children before and after they have completed the program against a change in adjustment over the same time period for an equivalent group of children who had not participated in any therapy. The children who went through the program showed significantly greater increase in social adjustment functioning over time. The research design is

A) comparison-group before-after.
B) single-group before-after.
C) comparison-group.
D) experimental.