Which of the following situations would combine to make zero?
OA. Last month, Carla worked for 25 hours in day shifts in a supermarket. She also worked for 25 hours in evening shifts.
OB. A hot air balloon rises 300 feet into the air. The balloon then descends by 300 feet before it lands.
OC. Before Jim started his trip, he filled 12 gallons of gas in his car's fuel tank. Later, during the trip, he filled another
12 gallons.
OD. A town library adds 800 books through purchases. Later, during a donation drive, it receives 800 books.