Question

    It’s easy to think that the globe’s vast oceans would be effective barriers to the movement of land animals. An elephant can’t swim across the Pacific, after all. But it turns out that plenty of plants and animals have unintentionally floated across oceans from one continent to another. Now comes evidence that tiny, trapdoor spiders (蜘蛛) made such a journey millions of years ago.

Moggridgea rainbowi spiders can be found on Kangaroo Island, which sits off the south coast of Australia. These spiders build a silk-lined hole in the ground, notes Sophie Harrison, a biologist in Australia. The hole and trapdoor provide these spiders with shelter and protection. It also provides them an out-of-sight spot from which to wait for approaching creatures.

There is evidence, though, that the ancestors of them might have traveled millions of meters to get to Australia from Africa. That isn’t as unlikely as it might at first seem. Australia used to be connected to other continents, long ago, as part of a supercontinent called Gondwana. And humans have been known to transport species all over the planet. But there’s a third option. The spiders might have rafted (乘筏) long distances across the sea.

To figure out which story was most likely true, Harrison and her colleagues looked at the spider’s genes. They looked at the genes in seven Moggridgea rainbowi spiders from Kangaroo, and five species of Moggridgea spiders from South Africa. The Australian and African spiders split off from a common ancestor some 2 million to 16 million years ago, the genes showed.

If a large swatch of land washes into the sea, filled with arachnids (蛛形纲动物), the spiders may be able to hide themselves throughout the journey. Plus, they can “hold their breath” and survive on stored oxygen during periods of temporary flooding, the researchers note.

1.What is the common belief about land animals according to the text?

A.They are sensitive to natural disasters.

B.They are unlikely to move across oceans.

C.They can’t make a long ocean voyage.

D.They float across oceans accidentally.

2.What does the underlined word “them” in Paragraph 3 refer to?

A.Biologists. B.Australians.

C.The spiders. D.The creatures.

3.How did the researchers conclude Australian and African spiders are from a common ancestor?

A.By comparing their genes.

B.By observing their living habits.

C.By making changes to their genes.

D.By studying their physical characteristics.

4.What could be the best title for the text?

A.These Spiders Traveled Globally to Hide Themselves

B.These Spiders Became More Adaptive When Traveling

C.These Spiders Crossed an Ocean to Australia for Survival

D.These Spiders Crossed an Ocean to Become Australians naturally

Answer

1.B

2.C

3.A

4.D

【解析】

这是一篇说明文。文章主要介绍了几百万年前，蜘蛛就从非洲漂洋过海来到了澳洲。

1.细节理解题。根据第一段中It’s easy to think that the globe’s vast oceans would be effective barriers to the movement of land animals.可知，人们很容易认为地球上广阔的海洋将是陆地动物迁徙的有效障碍。由此可知，人们认为陆地动物不可能跨越海洋。故选B项。

2.词义猜测题。根据第一段中Now comes evidence that tiny, trapdoor spiders (蜘蛛) made such a journey millions of years ago.可知，现在有证据表明，微小的活板门蜘蛛在数百万年前就开始了这样的旅程。由此可知，此处的代词them指代的就是蜘蛛。故选C项。

3.细节理解题。根据第四段中To figure out which story was most likely true, Harrison and her colleagues looked at the spider’s genes.可知，为了找出哪种说法更有可能是真的，哈里森和她的同事们研究了蜘蛛的基因。由此可知，科学家通过基因对比得知澳洲蜘蛛和非洲蜘蛛起源于同一个祖先。故选A项。

4.主旨大意题。根据文章内容，特别是第一段中But it turns out that plenty of plants and animals have unintentionally floated across oceans from one continent to another.可知，但事实证明，大量的植物和动物无意中从一个大陆漂洋过海到另一个大陆。由此可知，本文主要介绍了几百万年前，蜘蛛就从非洲漂洋过海来到了澳洲。故选D项。