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  3. How sharks navigate the vast and seemingly featureless ocean has long been a

How sharks navigate the vast and seemingly featureless ocean has long been a

游客2024-01-14  77
问题     How sharks navigate the vast and seemingly featureless ocean has long been a mystery. Now there’s evidence they may follow their noses. Sharks rely on their sense of smell to help chart a path through the ever-shifting waters of the deep seas, according to a new study. Scientists have supposed that the animals navigate by monitoring smell clues or the Earth’s magnetic field, but no one knew for sure.
    In new experiments near San Diego, scientists ferried wild leopard sharks about 6 miles (10 kilometers) away from their preferred habitats, fitted them with tracking devices, and stuffed some of the animals’ noses with cotton balls. "Just 30 minutes after being released facing the wrong way, sharks with full use of their smells made a corrective U-turn and then headed straight back to shore, " says study leader Andrew Nosal, a researcher at the Scripps Institution of Oceanography, California.
    Sharks with stuffed noses, meanwhile, "appeared lost", wandering aimlessly and swimming more slowly than those that could smell freely. To test sharks’ sense of direction, Nosal and colleagues captured several dozen leopard sharks, a small species found along the coast from Washington State to northern Mexico.
    After blocking some of the animals’ noses, the scientists then took the animals on a cruise to deeper waters before slipping them, safe and unharmed, back into the sea. Even the sharks with plugged noses made it partway back to shore before their tracking devices fell off. But those with unplugged noses "took very straight paths" toward home. Nosal supposes the sharks likely sniffed out chemical molecules found in higher and higher doses nearer to land.
    Other scientists, however, remain unconvinced. Maybe the animals with plugged noses "were confused by the fact that they had something stuffed in their nose," says Kim Holland, a marine biologist at the University of Hawaii at Manoa. It’s also unlikely the animals were following a smell that grew stronger closer to land, adds Jayne Gardiner, a sensory biologist at the New College of Florida. Animals that couldn’t smell a thing still turned toward the beach, which "suggests something else is really guiding them", she says.
    Study leader Nosal responds that sharks with cotton-stuffed nose willingly eat, suggesting that a congested nose doesn’t upset them much. He agrees that sharks use a variety of markers to find their way, "but the point is that smell participates in navigation, " he says, "Our study was only the first step in solving this mystery. " [br] This passage is mainly about________.
选项 A、why sharks have a good sense of smell
B、why sharks are clever animals
C、how scientists do the experiment
D、how sharks find their way in the vast ocean
答案 D
解析 根据文中第一段前三句“How sharks navigate the vast and seemingly featureless ocean has long been a mystery. Now there’s evidence they may follow their noses. Sharks rely on their sense of smell to help chart a path through the ever-shifting waters of the deep seas, according to a new study. ”可知，这篇文章主要讲的是鲨鱼如何在浩瀚的海洋中找到自己的路，故选D。
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