heard.1.AAMake sounds to meet humans.BBUse smoke to get rid of the bees.CCReward humans with pieces of nest.DDTake humans to find honey in the nest.答案:D听力原文:Humans have trained many different animals to help them. Usually these animals are dogs, horses and even dolphins. However, in Africa, humans have wild birds to help them find honey. In an unusual relationship, birds have learnt to take humans to find bees. They fly from tree to tree and make sure the humans are following them to the nest. Then the humans use smoke to get rid of the bees so they can get their honey safely. The humans reward the birds with pieces of the nest, which they love to eat. The birds don't like the honey, so it's a perfect situation for the humans who want only the honey. These small birds benefit because only humans can make it safe for the birds to get the food they want. Without the humans, the birds would be bitten by the bees and probably die. This relationship is really special because humans call for the birds. The humans make specific sounds with their voices when they are ready to look for honey, and the birds hear the sound and come. The humans do not use this sound for anything except to call for the birds. Researchers discovered that the birds understood the sound and arrived to help most of the time. And they were extremely successful finding the bees' nest for humans. When the researchers tested the birds with different sounds, the birds did not respond in the same way. They seem to recognize the language for finding honey. This is remarkable. This relationship is amazing because these are wild birds. They have not been trained by humans to do this. They have learnt this behaviour from years and years of working with humans. Humans have also given the knowledge about these special birds to their children, and so the tradition continues. Questions:1. What do these wild birds do to help humans?2. What is a fact about these small wild birds?3. What did the researchers discover about these birds?4. What is the main idea of this passage?