population.

　　To identify the blue whales，the researchers looked at photos of cetaceans taken in the North Pacific Ocean and compared them with a library of blue whale pictures taken along the west coast of the United States and Southern Pacific.Up to now，the researchers are not quite sure why the whales are changing their migration patterns，but they suspect that the whales may be following their food moving farther north by the changes in ocean conditions.

　　【语篇解读】　本文主要讲的是蓝鲸的迁移以及有可能引起迁移的原因。

　　4．According to the passage，blue whales are ________．

　　A．following a fixed route of migration

　　B．dying out due to commercial whaling

　　C．moving from the south to the north

　　D．rarely found in the Southern Pacific

　　解析：推理判断题。根据最后一段最后一句中的"the whales may be following their food moving farther north"可推出，蓝鲸正从南向北移动。故选C。

　　答案：C

　　5．The whale population in the North Pacific ________．

　　A．is different from the California population

　　B．is probably part of the California population

　　C．has become the largest group since the 1970s

　　D．has lived there since the 1960s

　　解析：细节理解题。根据第四段中的"But the current study shows that whales off the coast of British Columbia and the Gulf of Alaska are likely part of the California population"可知，选B。

　　答案：B

　　6．The underlined word"cetaceans"in Paragraph 5 probably means ________．

　　A．land creatures B．whale species

　　C．ocean conditions D．migration patterns

　　解析：词义猜测题。根据第五段中的"To identify the blue whales，the researchers looked at photos of cetaceans taken in the North Pacific Ocean"可知，为了辨认蓝鲸，研究者看在北太平洋拍的有关cetaceans的照片，所以cetaceans应该指的是鲸类。故选B。

　　答案：B

　　7．What might make blue whales migrate according to the researchers?

　　A．Commercial whaling. B．Weather conditions.

　　C．Life reproduction. D．Food resources.

　　解析：推理判断题。根据最后一段中的"but they suspect that the whales may be following their food moving farther north"可知，研究者怀疑蓝鲸有可能跟随着它们的食物向北移动。故选D。

　　答案：D

　　C

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