单选题
Most birds live in places where it is (36) during the day. They can use their (37) to see where they are (38) . The oilbirds of South America live in (39) caves. They use their ears to help them find their (40) . The oilbird is a brown bird (41) owl-like eyes. It nests on a high ledge in an ink-black cave. It (42) leaves the cave at (43) to hunt for food and returns before (44) The oilbird flies (45) circles in its dark cave. There is not enough (46) for it to see clearly with its large eyes. As the oilbird (47) , it uses its (48) to make sharp, clicking sounds. These clicks bounce off the cave walls and (49) echoes. The oilbird listens to the (50) it has made. If the echoes (51) a long time to come back, the bird knows it is (52) the wall. If they return (53) , the bird is close to it. (54) this way, the oilbird hears how far it is from the wall. Oilbirds (55) their lives in the dark, yet they never bump into the walls of their cave homes. We say that oilbirds "see" with their ears.