Research on the Stages of Transtheoretical Model Has Indicated That

Research on the stages of transtheoretical model has indicated that

A) there is little or no support for the validity of this model
B) people tend to change their behaviours after going through only one complete cycle of the stages
C) people only move forward through the stages as they change their behaviours
D) people tend to move forward and backward through the stages as they change their behaviours