The term that best describes what Joe should use to keep moving forward is "D. Implementation intentions".
Implementation intentions are plans that specify the 'when', 'where', and 'how' of an individual's goal-directed responses. This strategy involves not only setting a goal (e.g., improving a grade) but also planning out in detail when, where, and how he will achieve this goal. For example, Joe might set an intention to spend an extra hour each day reviewing his language arts assignments or to visit his teacher's office hours once a week for extra help.
This approach helps make his goals more concrete and action-oriented. Additionally, by planning out when and where he will work towards his goal, Joe can create a strong link in his mind between a specific situation or cue and his goal-directed response, making it more likely that he will follow through with his intentions.
It's also worth noting that process visualization might also be helpful in this situation. Process visualization involves envisioning the steps needed to achieve a goal, which can help Joe plan for potential obstacles and prepare strategies for overcoming them.