Summary Listen to the passage. For questions 26 ~30, complete the notes using no more than three words for each blank. The pr

Summary
   Birds have always been a problem for airplanes, (26)but now the problem of "bird strikes" is getting worse. Large airplanes can easily continue flying after hitting a bird weighing up to 2kg, but 30% of strikes involve birds which weigh more than this. Smaller birds can also be a danger, as they tend to fly in flocks. (27)Therefore, a plane may hit many birds at one time, increasing the danger of a plane crash.
   There are several reasons why bird strikes are happening more often. First, there are more airplanes flying than ever before. Second, most countries are taking steps to protect birds and other animals, so bird populations are increasing. Third, more modern airports are being built in the countryside, where bird populations are high. Unfortunately, instead of being frightened of airplanes, birds are attracted to airports as they provide a source of food, shelter, and warmth.
   There are three basic ways that airports try to lower the possibility of bird strikes. (28)The first is to change the airport’ s environment to make it less attractive to birds. This means decreasing the number of places where birds can find food by clearing up all garbage and cutting the grass short. (29)Another way is to use special fireworks called "bird bombs" which make loud noises and frighten the birds. Finally, if the birds are still attracted to the airport and cannot be frightened away, they are killed. One airport in Slovakia uses hawks to hunt smaller birds.
    (30)Killing birds is not a long-term solution, however. We must keep trying to find a way to make the sky a safe place for both airplanes and birds.