Scientists have been puzzled by the phenomenon that migrating birds fly not just in groups all the time, but in 'V' formations and they have tried to figure out what benefit birds get from this particular formation. Now, a research group from University of London may have found the answer ― migrating birds fly in a 'V' to save energy, according to a study published in the journal Nature. When a bird flaps(振翅) its wings, it stirs the air around it and causes it to move indifferent directions. Scientist found in the study that the air creates an upward-moving wave at the tips of the wings, which means that if a bird flies around the wingtips of another bird, it can get a boost（抬高） from the rising air and therefore use less energy to stay in the air. Apart form the 'free ride' strategy, scientists were also surprised to observe that migrating birds timed their wing beats and adjusted their positions in a very precise way to maximize the lifting effect while avoiding areas where the air move downward. 'They're able to sense what's going on from the bird in front, where this 'good air' is coming from and now how to position themselves perfectly in it,' lead researcher Steven Portugal told BBC. In fact, the 'V' formation has long thought to help birds fly more efficiently(效率搞地). A previous study showed that birds' heart rates went down when they were flying together in a 'V' formation. Jet fighters were also found to be able reduce their energy use by up to 18% by staying near the wingtips of other jet fighters. Both of these findings led scientists to suspect that the 'V' formation had an efficiency purpose, but until now they still lack proof. 'For scientists, the new study provides an insight into an interesting natural phenomenon. But it could mean even more for aircraft companies — helping them understand how they can imitate that with their plane formations to save fuel, said Portugal.' 小题1:What is the author's purpose in writing this article? A．To explain how birds benefit from migration. B．To introduce how migrating birds find their way. C．To tell some applications of migrating birds' 'V' formations. D．To report new findings about migrating birds' 'V' formations. 小题2: According to the recent study, when birds migrate . A．they don't change their lead birds during the whole journey B．they fly in 'V' formations to protect themselves against enemies C．they form the shape of a 'V' to make best use of the lifting effect D．the air they stir around makes it hard for the birds behind to fly fast 小题3:What is the significance of the new study according to this article? A．It might inspire aircraft companies to think of ways to improve efficiency. B．It has proved that the 'V' formation can improve in efficiency in many fields, C．It has led scientists to discover that birds' heart rates go down when they fly in a 'V'. D．It shows that the best formation of jet fighters in battle should be a 'V' formation. 小题4: The underlined word 'imitate' in the last paragraph most probably means ' '. A．use B．copy C．change D．learn