15．Blue whales are the largest animals ever known to have existed on the planet，and they can grow to a length of 100feet and weigh more than 330，000pounds．But recently researchers have found that these whales are on the move and they have migrated （moved） from California waters to areas off Canada and Alaska for the first time since commercial whaling ended in 1965．
The researchers identified 15blue whales that have appeared off the coast of British Columbia and the Gulf of Alaska since 1997．Four of these whales were recognized as ones that were once sighted off California shores，suggesting that the whales are returning to an old migration pattern between the coasts．
Before commercial whaling began in the early 1900s，blue whales were found widely throughout the North Pacific and California waters．But from the 1920s to the 1960s，whaling severely reduced the whale populations．Blue whales never recovered in the Northern Pacific，making sightings in this area rare．However，much larger groups of whales have been observed close to California since the 1970s．
The scientists had previously thought that the California population was separate from the population that had historically lived in North Pacific waters．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．
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．
28．According to the passage，blue whales areD．
A．following the fixed route of migration
B．dying out due to commercial whaling
C．rarely found in the Southern Pacific
D．moving from the south to the north
29．The whale population in the northern PacificC．
A．is different from the California population
B．has become the largest group since the 1970s
C．is probably part of the California population
D．has lived there since the 1960s．
30．The underlined word"cetaceans"in Paragraph 5probably meansA．
A．whales species B．land creatures
C．ocean conditionsD．migration patterns
31．What might make blue whales migrate according to the researchers？B
A．Commercial whaling．B．Food resources．
C．Weather conditions．D．Life reproduction．
分析 本文主要講述了科學家們對藍鯨的研究，藍鯨作為我們所熟知的最大的動物，近日正在由南向北遷移，并且研究人員已經在哥倫布比海岸發現了藍鯨的行蹤．
解答 28．D細節理解題．根據第一段But recently researchers have found that these whales are on the move and they have migrated （moved） from California waters to areas off Canada and Alaska for the first time since commercial whaling ended in 1965．可知最近研究發現這些藍鯨從加利福尼亞遷徙到加拿大和阿拉斯加，即由南向北遷移．故選D．
29．C細節理解題．根據第三段blue whales were found widely throughout the North Pacific and California waters．But from the 1920s to the 1960s，whaling severely reduced the whale populations．Blue whales never recovered in the Northern Pacific，making sightings in this area rare可知藍鯨在北太平洋和加利福尼亞到處都是．但在二十世紀二十年代到六十年代，數量急劇減少，在北太平洋很好看到藍鯨了．由此可知，北太平洋的鯨魚很可能是加利福尼亞的一部分．故選C．
30．A詞義辨析題．根據第五段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．可知為了分析藍鯨，研究者看了北太平洋的鯨的照片，與美國西海岸的鯨的圖書館的照片進行對比．由此可知，"cetaceans"的意思是"鯨魚物種"．故選A．
31．B細節理解題．根據最后一段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．可知直到現在，研究者不確定為什么藍鯨要改變他的遷徙方式．但他們懷疑藍鯨可能是隨著食物的變化而進行流動的．故選B．
點評 本文考察學生的理解推斷能力以及細心程度，只要抓住文章的關鍵詞，采用尋讀的方法查找細節，就能找到正確答案．
