The best way to fix a run-on sentence is to add a comma, conjunction, or period. In this case, separating the sentence into 2 with a period is the best option:
Justin rushed through the obstacle course. He couldn't make it over the final obstacle in time.
Hope this helps! Good luck! :)
Answer:
Justin rushed through the obstacle but, he couldn't make it over the final obstacle in time.
Explanation:
Just add a conjunction to run on sentences.
