What Is the Major Distinction Between the Group Research Design

What is the major distinction between the group research design and the single-subject research design?

A) The group research designs measure client behavior using two different scales that are designed to measure the target behavior.
B) The single-subject designs measure client behavior using two different scales that are designed to measure the target behavior.
C) The single-subject design measures target behavior repeatedly for a single client, whereas the group design measures a group of people on the target behavior.
D) The group research design is used only when you are using a group treatment, such as a support group for the victims of violence.