A、Urban expansion. B、Land expansion. C、Agricultural expansion. D、Industrial expansion. B新闻末尾部分提到，关键栖息地被用于土地复垦(many of these crit

Scientists say a huge percentage of bird species are in danger because their habitats, or homelands, are disappearing.
   Traditional migration paths take birds through countries that are not protecting locations to stop, rest and feed.
   The scientists studied the migration, or flight, paths, of almost 1,500 species. They decided that 91 percent of them passed through dangerous areas.
   The major danger for migratory birds is development. Building and paving has covered over nature where birds stop and feed as they move from one part of the world to another.
   For example, a bird called the bar-tailed godwit migrates from its breeding grounds in the Arctic. It flies all the way to the southern hemisphere in Australia and New Zealand. Along the way, the small birds stop at Yellow Sea mudflats in China, North Korea and South Korea.
   One of the scientists who worked on the study says "many of these critical sites have been lost to land reuse owing to urban, industrial and agricultural expansion."
5. Why are bird species in danger according to the news report?
6. What do we learn about migratory birds from the news?
7. What is the reason for the lost of critical sites for migratory birds?