Answer:
This is an example of demotivation.
Explanation:
The student worked hard every night to deliver the homework on time and completely answered, but when the teacher did not collect the answered homework, the student felt that his effort and time spent to answer it was in vain. This discouraged the student from continuing to answer his homework and for this reason, he stopped responding, since he knows that the teacher will not collect it and will not evaluate the answers he gave.