Final answer:
The correct homonym to use in the sentence is 'then' as it indicates a sequence of events or time.
Step-by-step explanation:
In the given sentence, the correct homonym to use is then.
'Then' is used to indicate a sequence of events or time. In the given sentence, the word 'then' is used to show that the student will do their science homework after completing their math homework.
Example: 'First, I will eat dinner, and then I will watch a movie.'
Learn more about Homonyms