Passage C
　　This is a story about one kind of sea mammal(哺乳动物), big business, fishing boats, sandwiches and kids.
　　Fishermen catch big tuna(金枪鱼) for the canning companies.They used to set out their nets when they saw dolphins(海豚), which often swim with tuna.
　　When tuna swam into the nets, dolphins were also caught.They could not escape to the surface to breathe air.Before fishermen could pull in the nets, the dolphins had drowned.
　　People interested in dolphins protested at this practice.They asked everyone to persuade the big tuna-canning companies to stop the killing.
　　Many kids sent letters to the companies that buy tuna from fishermen.Their message was clear —protect dolphins, or the cans of tuna will stay on supermarket shelves!
　　The result? Tuna companies saw that their profits would become less if kids and their families stopped buying tuna.They worked out ways that, with extra time and effort, let fishermen catch tuna but not dolphins.
　　Now it costs a little more for a tuna sandwich.But most kids agree it’s worth it to share the world with dolphins!