57. Joplin’s 5-stage model was created to be intentionally simple and define learning but is not a learning theory itself. The model is organized around a “hurricane-like cycle” emphasizing a challenging action in between focusing and debriefing. These “action-reflection” cycles are differentiated from experience alone by incorporating a reflection process. The application of the cycles can be in either a “maxi” or “mini” scope, depending on the intent of the project； the cycle can focus on large-scale course design or a brief teaching moment or insight. Which stage of Joplin’s model of experiential learning is characterized by “challenge”?
(A) focus
(B) action
(C) feedback
(D) debrief