If you take a part-time job while you are still in school, what might your opportunity cost be?

Your opportunity costs might be worse grades overall, as you'll have less time to devote to school. You will have less time on your hands due to having to work, even a small amount of time. There will be upfront costs for transportation so one opportunity cost might be weighing the profits of the job, over the cost for transportation to that job.

"germany's geographic location was an advantage when it was on the offensive in the war because it was situated next to an extremely wide river, the rhine, which was difficult for the allies to cross."