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A number of whales die every year because of "beaching": they swim onto a beach or a shore in general and become stranded there, unable to return to the sea. The reason that some whales become beached remains unclear, however. Scientists have proposed several theories to explain it. First, some scientists believe that beaching occurs when whales are sick from a parasite, poison, or disease. These scientists argue that seriously ill whales may become confused about the direction in which they are swimming. This can cause them to swim too close to the shore and become trapped on the beach. Second, other researchers suggest that powerful sonar used by military ships may cause beaching. Sonar is a navigational tool that sends sound waves of a certain frequency into the water. Scientists have noticed that more whales than usual are found beached after military sonar tests have been conducted in an area. They speculate that the sonar may be interfering with the whales' system of echolocation, the process by which whales send out their own sounds for navigating and finding food. Military sonar is much stronger than whales' echolocation and may interfere with the whales' ability to navigate, causing them to beach. Third, still other researchers believe that whales become beached because of disturbances in Earth's magnetic field. This explanation is based on the idea that whales orient themselves and navigate by the position of Earth's magnetic field. Supporters of this theory point out that magnetic field changes can occur before earthquakes and that there have been reports of numbers of whales becoming beached before major earthquakes in some areas. Changes in the magnetic field leading up to an earthquake may confuse whales and cause them to swim to land.

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None of the theories presented in the reading passage can explain whale beaching because each explanation leaves out some important information. First, the sickness theory, it makes sense that sick whales could become disoriented and end up trapped on land. But if this were a significant cause of beaching, we would expect most Beached whales to show signs of sickness. But when scientists examine the bodies of whales that have died from beaching, this is not what they find. In fact, the whales are usually found to have been free of serious disease at the time of their death. So sickness doesn't solve the mystery of whale beaching. Second, about military sonar, there seems to be some confusion in the reading passage during the sonar tests mentioned in the passage, the military used what's called a mid-frequency sonar, which uses sound waves from the middle of the sound frequency range. However, whales use low frequency sound waves for echolocation. It's unlikely that a mid-frequency military sonar would interfere with low frequency whale echolocation. These are two very different ranges of sound frequencies. So if there is any effect that military ships have on whales, it's not caused by the sonar. Third, the fact that whales sometimes beach during the periods of magnetic disturbances before earthquakes, does not necessarily prove that whale beaching’s and earthquake disturbances are closely linked. A lot of earthquakes occur every year, and many of them are not preceded by beaching’s. And it's also true that many beaching’s happen when no earthquakes are taking place. So the evidence for the magnetism theory is really pretty weak, just some isolated incidents and no regular correlation.
问题

Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.

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  • The lecture casts doubt on the three theories presented in the reading passage regarding the causes of whale beaching. The professor argues that each explanation is flawed or lacks substantial evidence.

     

    Firstly, the reading suggests that whale beaching may occur due to sickness, with sick whales becoming disoriented and swimming onto the shore. However, the professor counters this by noting that scientific examinations of beached whales usually reveal no signs of serious illness that researchers can identify. This lack of conclusive evidence indicates that sickness is unlikely to be a significant factor in beaching.

     

    Secondly, the reading proposes that military sonar may interfere with whales' echolocation, leading to beaching. The professor disputes this theory by explaining that the sonar used in military tests operates at mid-frequency, whereas whales use low-frequency sounds for echolocation. Since these are different frequency ranges that casts two different soundwaves, it is unlikely that military sonar would disrupt whales' ability to navigate.

     

    Lastly, the reading claims that changes in the Earth's magnetic field, particularly before earthquakes, might confuse whales and lead them to beach. The professor challenges this idea, pointing out that there is no consistent correlation between magnetic disturbances and whale beaching, as many earthquakes occur without any corresponding beaching events, while many beaching happen when no earthquakes are happening afterwards.

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