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    課程推薦：2015職稱英語 鎖定65分 沖擊75分

　　2015年職稱英語理工類B級補全短文練習題(4)

　　Migration of Monarch Butterflies

　　One of the greatest mysteries in biology―how the monarch butterfly travels thousands of kilometers on its yearly migration―has just been solved.

　　(1)No other butterfly in the world migrates like the orange and black monarchs of North America.(2)Each autumn,thousands travel up to 3,000 km to spend the winter in the mountains of Mexico.There are so many,they almost block out the sky,and you can hear their wings beating.

　　It usually takes the butterflies two months to reach Mexico.After staying five months,they head back up north in the spring.But not one butterfly finishes the whole round-trip.(3)Three generations of butterflies will live and die during the spring journey alone.The fourth and final generation of the year is born in early autumn and will reach the north.But it hardly gets to rest before starting the long journey south to Mexico.

　　The most amazing thing about these butterflies is that they return to the very same tree in Mexico that their great-great-grandparents used the winter before.Past studies have shown that the insects use the sun as a compass to show them the way.(4)This new study now shows that the insects use a "circadian(生理節奏的)" clock in their bodies as part of their sun compass.In laboratory tests,monarch butterflies were found to fly in the right direction under normal daylight hours.But those flying in 24-hour light headed straight towards the sun.(5)Scientist Steven Reppert,who led the research,said: "We have shown the need for the circadian clock for monarch butterfly migration.When the clock is interrupted,monarchs are unable to fly towards Mexico."

　　A.That is,they no longer had any sense of time.

　　B.They lay eggs along the way and die.

　　C.The circadian clock is useful for monarch butterfly migration.

　　D.Monarch butterflies use the sun to set their body clocks and make their journeys,according to US scientists.

　　E.But experts are unsure how the butterflies change their direction as the sun moves in the sky.

　　F.They cannot live for long periods in cold weather.

　　解析：

　　1.D，前一句提到有關蝶王的謎已經解開。本句詳細闡述這個謎底是什么，即美國科學家發現蝶王根據太陽設定自己的生物鐘去旅行

　　2.F，后一句提到每年秋天成千只蝴蝶長途跋涉到墨西哥山脈過冬。因此本句是個銜接句，說明在寒冷的天氣這些蝴蝶生活的時間不會很長。

　　3.B，前一句提到沒有一只蝴蝶可以完成全程旅行。本句更進一步說明蝴蝶的旅行途中發生的事情。

　　4.E，前一句說過去的研究表明有些昆蟲利用太陽指引方向。后一句詳細介紹有關蝴蝶如何利用太陽指引方向。所以本句是轉折句，表明老師們不確定蝴蝶是如何利用太陽指引方向的。

　　5.A，本句進一步解釋前一句話的內容。前一句話意為“蝴蝶在24小時都有燈光的情況下，會直接飛向太陽”。本句意為“這說明這種情況下蝴蝶沒有時間概念”。That is,意為“也就是說”。

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