剑桥雅思9全真试题听力部分 Test1(4-1)

作者:未知 来源:未知 2015-06-13 我要评论( )

    TEST 1

    SECTION 4-1

    Good afternoon everyone.Well,with some of you about to go out on field work it's timely that in this afternoon's session I'll be sharing some ideas about the reasons why groups of whales and dolphins sometimes swim ashore from the sea right onto the beach and,most ofter,die in what are know as 'mass strandings'.

    Unfortunately,this type of event is a frequent occurrence in some of the locations that you'll be travelling to,where sometimes the tide goes out suddenly,confusing the animals.However,there are many other theories about the causes of mass strandings.

    The first is that the behaviour is linked to parasites.It's often found that stranded animals were infested with large numbers of parasites.For instance,a type of worm is commonly found in the ears of dead whales.Since marine animals rely heavily on their hearing to naviqate this type of infestation has the notential to be very harmful.

    Another theory is related to toxins,or poisons.These have also been found to contribute to the death of many marine animals.Many toxins,as I'm sure you're aware,originate from plants,or animals.The whale ingests these toxins in its normal feeding behaviour but whether these poisons directly or indirectly lead to stranding and death,seems to depend upon the toxin involved.

    In 1988,for example,fourteen humpback whales examined after stranding along the beaches of Cape Cod were found to have been poisoned after eating tuna that contained saxitoxin,the same toxin that can be fatal in humans.

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