She should conclude that:
D. Staying after school is reinforcing for Eric.
Step-by-step explanation:
The reinforcer can be something that the punisher thinks will decrease the unwanted behavior but there are times when that is not the case.
If Eric does not see the school stay back as bad or gets irritated by it instead of learning from it, it does not help hi in a way that it should have to curb his swearing.
Thus the teacher needs to find a different way to curb his swearing because this punishment is only helping that habit.