Final answer:
Constructive alternativism is the determinant of decisions and behavior according to the concept of personal constructs, where individuals create and adjust their constructs as they interpret their environment.
Step-by-step explanation:
An important determinant of one's decisions and behavior, according to the concept of personal constructs, would be B. Constructive alternativism. This concept, associated with George Kelly's Personal Construct Theory, suggests that we can revise or replace our constructs with alternatives to better understand and predict the world around us. Our experiences and the outcomes of our behaviors help to shape these personal constructs, thereby influencing our future decisions and behavior. This idea aligns with psychological approaches that emphasize personal agency and the interpretative role of the individual in understanding their environment.