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Among the dead in South Asia's tsunami① were many tourists at Sri Lanka's national wildlife park at Yala. But very few of the park's animals - elephants， buffaloes， monkeys and wild cats - appear to have died. There are theories that animals can sense natural disasters and flee to safety.

First， it's possible that the animals may have heard the quake before the tsunami hit. The underwater rupture likely produced sound waves known as infrasound② or infrasonic sound. Humans can't hear infrasound， but many animals including dogs， elephants， tigers and pigeons can. A second early warning sign the animals might have sensed is ground vibration③。 The massive quake would have produced vibrational waves known as Rayleigh waves. These vibrations move through the ground like waves move on the surface of the ocean but faster. They travel at ten times the speed of sound. The Rayleigh waves would have reached SriLanka hours before the water hit. Mammals④， birds， insects and spiders can sense Rayleigh waves. So the animals at Yale might have felt the Rayleigh waves and then run to higher ground. But what about humans？ While we can't hear infrasound， we can feel it， although we don't necessarily know we're feeling it. We also experience Rayleigh waves by special sensors in our joints⑤， which exist just for that purpose. Sadly， it seems we don't pay attention to the information when we get it. Maybe we screen it out because there's so much going on before our eyes and in our ears. Humans have a lot of things on our minds and usually that works out OK.

Vocabulary:

   ① tsunami  n. 海嘯

    ② infrasound  n. 次聲

③ vibration  n. 振動，顫動

④mammals  n.哺乳動物

⑤joint    n.關節

Choose the best answers according to the above：

  1. Why did few animals at Yala die when the tsunamis that caused a huge number of human deaths hit？

    A. Because the animals were staying at a higher place in the park.

    B. Because the animals were able to run much faster than human beings.

    C. Because human beings cannot hear the infrasonic sound.

    D. Because the animals might have picked up the danger signals and ran away.

    2. Which of the statements about "Ravleigh waves" is true？

A. Rayleigh waves are massive vibrational waves that usually cause quakes or tsunamis.

    B. Rayleigh waves move on the ocean surface at a speed ten times that of sound waves.

    C. Rayleigh waves can be felt both by animals and human beings.

    D. Rayleigh waves， just like infrasonic sound， can only be felt by animals.

   3. When a tsunami hits， it is possible that ＿＿＿＿

    A. we can't feel the infrasound so we can't be informed of the danger

    B. we can feel Rayleigh waves as well as infrasound so we are able to escape the danger like animals

    C. we were so busy with things on our minds that we feel neither infrasound nor Rayleigh waves

    D. we think nothing of the information of its coming even though we can also get it

4. What does the underlined word "that" in the last sentence refer to？

    A. Screening out the information.

    B. There being so much going on before our eyes and in our ears.

    C. Having a lot of things on our minds.

   D. Paying attention to the information.

KEYS:

1. D  細節理解題。從第二、三段可知，動物能提前感知到危險臨近，逃到安全地方去

2. C  細節理解題。從第三、四段可知，人和動物都能感覺到Rayleigh waves.

3. D  細節理解題。從最后一段第四句可知。

4. A  詞義猜測題。該詞指代的意思從前一句Maybe we screen it out because …可以確定。

Background Information:

動物為什么會預報災難？科學上有以下幾點解釋和推測：

 第一，對超聲波和次聲波的感受。魚類和其他一些水生動物能感受到人所不能感受到的超聲波和次聲波。一般人所能感受到的聲波范圍為16 Hz~20 000 Hz，小孩可以達到 22 000 Hz，高于或低于這個聲波范圍就不能感受到。魚類內耳和身體兩側有側線感受器，這是一種機械感受器，能感受1~25 Hz的次聲波，即使對水流壓力的微小變化或微弱的水流波動也很敏感；水母（海蟄）的傘體邊緣有感覺球，能感受8~13 Hz的次聲波。漂浮在海面的水母，能在暴風到來之前，感受到由于流動空氣與波浪摩擦而產生的次聲波，因此及時離開淺海，避免了被巨浪砸碎的災難；在海洋中的海豚，能感受到50~100 000 Hz的聲波，又具有完善的聲納系統。因此，它能利用超聲波和次聲波正確地追蹤千米以外的魚群，并能分辨出種類。由此可見，魚類和其他一些水生動物在震前出現異常反應的原因，很可能是與強震前有超聲波和次聲波發生有關。此外，蝙蝠能感受1 500~150 000 Hz 的聲波。它的超聲定位系統極為優越，不僅分辨率高，而且抗干擾性強，能從比信號高出200倍的噪聲背景中接受小昆蟲身上反射回來的信號。因此，蝙蝠在地震前遷飛，是與感受超聲有關的。

  第二，對熱的變化的高度敏感。在地震前，穴居動物都有明顯的反應。例如，蛇類具有頰窩或感覺小窩，窩內的感覺細胞對“熱”極為敏感。有人用南美洲的蟒蛇做過實驗，在波長為10 600 nm的紅外線下熱量在0.084 J/cm2時，就有熱感覺反應。由此推測，蛇在震前的異常反應，可能與地熱變化有關。

  第三，對微弱的機械振動的感受。家禽和鳥類的腿部具有微小的感震體，它們憑此能感受到枝頭或地面上十分微弱的機械振動（幾十至上千赫）。中國科學院生物物理研究所曾做過這樣的實驗：把100只家鴿分作兩組，每只50組，將其中一組家鴿的感振小體和中樞神經之間相聯系的神經切斷。結果，在一次4級多的地震前，被切斷神經的一組基本上安靜如常，而另一組家鴿都驚飛了。這說明家鴿的感震小體能感受到震動的波動。在強震前，豬、牛、羊等家畜普遍出現異常反應的原因，可能與它們的腿部、趾部和腹部腸系膜等部位，分布著大量對機械振動非常敏感的環層小體有關。

  第四，對海水壓力的感受。在海嘯到來之前，往往會有一些深海魚類因受不了深海地震而引起的水溫驟升而逃命，因為這些深海魚類所處的生活環境，其水溫終年在0oc~ 2oc。由于溫度的劇變，無形中給深海魚類巨大的打擊，即使這些深海魚類逃到水面上，也是死路一條。因為深海魚類平時一直承受著海水的巨大壓力（水深每增加10 m就會增加101.3 kpa的壓力），如果突然到了水面上，由于海水的壓力驟然減小，會使它們的胃翻出口外，眼睛突出眼眶外，體內部分小血管破裂，最終導致死亡。因此，在淺海中游玩的人們，一旦看到一些怪模怪樣已經死去的深海魚類，就應當引起高度警覺，萬萬不可掉以輕心，這說明有可能過不了多長時間，兇猛的海嘯就會瘋狂席卷過來，在這里游玩的人們將會被無情的海嘯吞噬掉。因此，防患于未然是十分必要的。