Answer:
d.both of her grades to rise
Step-by-step explanation:
If her PPF has shifted inward, it means that the possible maximum values of her grades have fallen, whether she focuses on only one of the subjects, or on both.
For this reason, after an inward shift of her PPF, it is mathematically impossible for both her grades to rise. She might have one of the grades rise only if she focuses more on than subject than before the inward shift, but this would also result in a lower grade for her other subject.