In a Graph of Single-Subject Research Data,a Clear Indication of a Treatment

Multiple Choice

In a graph of single-subject research data,a clear indication of a treatment effect is

A) a continuation of the same average level from one phase to the next.
B) a continuation of a clear trend from one phase to the next.
C) a gradual change in behavior that becomes clear several observations after the treatment is initiated.
D) a clear and immediate change in either the level or trend when the treatment is initiated.