in which of these situations do the quantities combine to make 0? A. A dolphin swims 20 feet straight down from the surface. It then rises 20 feet to return to the surface. B. Scott earns $20 at his family's garage sale. He then earns $20 walking dogs for his neighbors. C. Travis receives $10 from a friend to pay for a concert ticket. He then spends $20 on tickets for his friend and himself. D. A scuba diver drops 30 feet below sea level. He then swims 30 feet across the ocean floor.