Final answer:
The correct preposition to use in this sentence is 'por'.
Step-by-step explanation:
The correct preposition to use in this sentence is por. When expressing the reason for not being hungry, the preposition por is used in Spanish. For example, 'No tengo hambre por haber comido recién' (I am not hungry because I just ate). In this case, the student is saying 'No tengo hambre por haber acabado' (I am not hungry because I just finished eating).
Learn more about Prepositions in Spanish