Answer the following question: Write a multi-choice question for the following article, with the given choices and answer: Article: High in the sky, a group of birds fly past. The 5-foot-tall creatures are whooping cranes, the tallest birds in North America noted for its loud call. The wild animals appear to be following much larger birds. But those aren't birds at all. They are three-wheeled aircraft called trikes , and the pilots flying them are wearing white helmets and white gowns. That plan might sound like a stupid idea, but it's not. The pilots are from an organization called Operation Migration. They are helping the whooping cranes learn to migrate, or move from one area to another when the seasons change. The cranes are endangered. In 1941,the species had dwindled to roughly 20 birds because of hunting and habitat loss. US wildlife officials counted 149 whooping cranes in November 1995,the most since the American government began taking censuses in the 1930s.Today,about 380 remain. In the fall, whooping cranes are supposed to migrate south. However, many of them don't know how. "With so few birds left, young whooping cranes typically don't have parents around to teach them," explains pilot Joe Duff. That's where the trikes come in. Each October, pilots dress up as whooping cranes and take to the skies in Wisconsin. The young birds follow them because they think the trikes are big whooping cranes. It takes about three months to reach south--with plenty of rest stops on the way. The pilots lead the cranes to refuges, or protected areas, in Florida. This spring, the birds will migrate north by themselves--no trikes needed! "It's nice because you know the birds are going to make it," Duff told WR News. Options: A are the tallest birds in the world B aren't birds at all C are increasing in the past 15 years D have no team spirit Answer: C are increasing in the past 15 years Question:
Answer:
We can learn from the passage that whooping cranes .