听力原文：W: What is the life span of dolphins? M: Maximum life span is different from average life span. The average life span for a bottlenose dolphin is about 25 years. For most species of dolphins we don't know what the average or maximum life spans are. W: What is the dolphin's favorite thing to eat? M: Most eat fish and squid and sometimes shrimp. What they eat at a given time may depend on what kind of fish or squid is easiest to get. W: How big are the dolphin babies? M: Bottlenose dolphin calves are about four feet long when they are born. W: Why are dolphins so intelligent? M: Lots of people think that dolphins are really smart but scientists don't have any information to prove it. Most dolphin biologists think that dolphins are about as smart as dogs and chimps. W: What is being done to save dolphins? M: Most whales and dolphins are net endangered. Those that are endangered have become so because humans have destroyed their habitat or affected their habitat in other ways. W: What is the biggest reason for dolphins' death at sea? M: For most species of dolphins the most common cause of death is probably natural disease. W: Really? M: Yes, but we don't really know what happens at sea, so we can't say for sure. However, for some species of dolphins the biggest cause of death may be entanglement in fishing gear like drift nets and purse seines. (20)