Final answer:
The preposition that should fill in the blank is 'in', indicating a duration of time.
Step-by-step explanation:
The preposition that should fill in the blank in the given sentence is in. So, the correct sentence would be 'I will be finished my work in an hour, Then, I can go home'.
The preposition 'in' is used to indicate a duration of time before an event or action happens. In this case, it shows that the student will be done with their work within a specific time frame, which is an hour.
By using the correct preposition 'in', the sentence conveys the intended meaning that the student will be able to go home after completing their work within the stated time period.
Learn more about Prepositions